SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                -----------------

                                  SCHEDULE 13G

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934
                               (Amendment No.) (1)

                                 NuVasive, Inc.
                                (Name of Issuer)

                    Common Stock, par value $0.001 per share
                         (Title of Class of Securities)

                                    670704105
                                 (CUSIP Number)

                                December 31, 2004
             (Date of Event Which Requires Filing of This Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

     |_| Rule 13d-1(b)

     |_| Rule 13d-1(c)

     |X| Rule 13d-1(d)

-----------
      (1) The remainder of this cover page shall be filled out for a reporting
person's initial filing on this form with respect to the subject class of
securities, and for any subsequent amendment containing information which would
alter disclosures provided in a prior cover page.

      The information required in the remainder of this cover page shall not be
deemed to be "filed" for the purpose of Section 18 of the Securities Exchange
Act of 1934 ("Act") or otherwise subject to the liabilities of that section of
the Act but shall be subject to all other provisions of the Act (however, see
the Notes).


<PAGE>

CUSIP No. 670704105                      13G                  Page 2 of 10 Pages

--------------------------------------------------------------------------------
1.   NAME OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

     William Blair Capital Partners VII QP, L.P.
--------------------------------------------------------------------------------
2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                                 (a)  |_|
                                                                 (b)  |_|
--------------------------------------------------------------------------------
3.   SEC USE ONLY


--------------------------------------------------------------------------------
4.   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
--------------------------------------------------------------------------------
  NUMBER OF    5.   SOLE VOTING POWER

   SHARES           0
               -----------------------------------------------------------------
BENEFICIALLY   6.   SHARED VOTING POWER

  OWNED BY          2,450,594 (See Item 4)
               -----------------------------------------------------------------
    EACH       7.   SOLE DISPOSITIVE POWER

  REPORTING         0
               -----------------------------------------------------------------
   PERSON      8.   SHARED DISPOSITIVE POWER

    WITH            2,450,594 (See Item 4)
--------------------------------------------------------------------------------
9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     2,450,594 (See Item 4)
--------------------------------------------------------------------------------
10.  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          |_|
--------------------------------------------------------------------------------
11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

     11.8%
--------------------------------------------------------------------------------
12.  TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------

                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


<PAGE>

CUSIP No. 670704105                      13G                  Page 3 of 10 Pages

--------------------------------------------------------------------------------
1.   NAME OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

     William Blair Capital Partners VII, L.P.
--------------------------------------------------------------------------------
2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                                 (a)  |_|
                                                                 (b)  |_|
--------------------------------------------------------------------------------
3.   SEC USE ONLY


--------------------------------------------------------------------------------
4.   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
--------------------------------------------------------------------------------
  NUMBER OF    5.   SOLE VOTING POWER

   SHARES           0
               -----------------------------------------------------------------
BENEFICIALLY   6.   SHARED VOTING POWER

  OWNED BY          2,450,594 (See Item 4)
               -----------------------------------------------------------------
    EACH       7.   SOLE DISPOSITIVE POWER

  REPORTING         0
               -----------------------------------------------------------------
   PERSON      8.   SHARED DISPOSITIVE POWER

    WITH            2,450,594 (See Item 4)
--------------------------------------------------------------------------------
9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     2,450,594 (See Item 4)
--------------------------------------------------------------------------------
10.  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          |_|
--------------------------------------------------------------------------------
11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

     11.8%
--------------------------------------------------------------------------------
12.  TYPE OF REPORTING PERSON*

     OO
--------------------------------------------------------------------------------

                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


<PAGE>

CUSIP No. 670704105                      13G                  Page 4 of 10 Pages

--------------------------------------------------------------------------------
1.   NAME OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

     William Blair Capital Management VII, L.L.C.
--------------------------------------------------------------------------------
2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                                 (a)  |_|
                                                                 (b)  |_|
--------------------------------------------------------------------------------
3.   SEC USE ONLY


--------------------------------------------------------------------------------
4.   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
--------------------------------------------------------------------------------
  NUMBER OF    5.   SOLE VOTING POWER

   SHARES           0
               -----------------------------------------------------------------
BENEFICIALLY   6.   SHARED VOTING POWER

  OWNED BY          2,450,594 (See Item 4)
               -----------------------------------------------------------------
    EACH       7.   SOLE DISPOSITIVE POWER

  REPORTING         0
               -----------------------------------------------------------------
   PERSON      8.   SHARED DISPOSITIVE POWER

    WITH            2,450,594 (See Item 4)
--------------------------------------------------------------------------------
9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     2,450,594 (See Item 4)
--------------------------------------------------------------------------------
10.  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          |_|
--------------------------------------------------------------------------------
11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

     11.8%
--------------------------------------------------------------------------------
12.  TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------

                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


<PAGE>

CUSIP No. 670704105                      13G                  Page 5 of 10 Pages

--------------------------------------------------------------------------------
1.   NAME OF REPORTING PERSONS
     I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

     William Blair Capital Management VII, L.P.
--------------------------------------------------------------------------------
2.   CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

                                                                 (a)  |_|
                                                                 (b)  |_|
--------------------------------------------------------------------------------
3.   SEC USE ONLY


--------------------------------------------------------------------------------
4.   CITIZENSHIP OR PLACE OF ORGANIZATION

     Delaware
--------------------------------------------------------------------------------
  NUMBER OF    5.   SOLE VOTING POWER

   SHARES           0
               -----------------------------------------------------------------
BENEFICIALLY   6.   SHARED VOTING POWER

  OWNED BY          2,450,594 (See Item 4)
               -----------------------------------------------------------------
    EACH       7.   SOLE DISPOSITIVE POWER

  REPORTING         0
               -----------------------------------------------------------------
   PERSON      8.   SHARED DISPOSITIVE POWER

    WITH            2,450,594 (See Item 4)
--------------------------------------------------------------------------------
9.   AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

     2,450,594 (See Item 4)
--------------------------------------------------------------------------------
10.  CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*

                                                                          |_|
--------------------------------------------------------------------------------
11.  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

     11.8%
--------------------------------------------------------------------------------
12.  TYPE OF REPORTING PERSON*

     PN
--------------------------------------------------------------------------------

                     *SEE INSTRUCTIONS BEFORE FILLING OUT!


<PAGE>

                                  SCHEDULE 13G

Item 1(a). Name of Issuer:

           NuVasive, Inc. (the "Company")

Item 1(b). Address of Issuer's Principal Executive Offices:

           10065 Old Grove Road
           San Diego, CA 92131

Item 2(a). Name of Persons Filing:

           This statement is filed jointly by each of the following Persons
           pursuant to Rule 13d-1(k) promulgated by the Securities and Exchange
           Commission ("SEC") under Section 13 of the Securities Exchange Act of
           1934, as amended (the "Act"): (i) William Blair Capital Partners VII
           QP, L.P., a Delaware limited partnership (the "Fund"), by virtue of
           its direct beneficial ownership of Common Stock and (ii) William
           Blair Capital Partners VII, L.P., a Delaware limited partnership (the
           "Fund"), by virtue of its direct beneficial ownership of Common Stock
           and (iii) William Blair Capital Management VII, L.L.C. ("WBCPCO,"
           together with the Fund, each a "Reporting Person" and collectively,
           "Reporting Persons"), a Delaware limited liability company, by virtue
           of its being the general partner of the Fund. (iv) William Blair
           Capital Management VII, L.P. ("WBCPCO," together with the Fund, each
           a "Reporting Person" and collectively, "Reporting Persons"), a
           Delaware limited liability company, by virtue of its being the
           general partner of the Fund. By virtue of being members of the Board
           of Managers of WBCPCO (the "Board"), Timothy Burke, John Ettelson,
           Robert D. Blank, David G. Chandler, Arda Minocherhomjee, Timothy M.
           Murray, and Robert Healy may be deemed to possess indirect beneficial
           ownership of the Common Stock, but such beneficial ownership is
           disclaimed. Only the Board, acting upon the consent of a majority of
           the members of the Board at any meeting of the Board where a quorum
           is present, possesses the right to vote, direct the vote, dispose or
           direct the disposition of the Common Stock. No individual has sole
           power to vote, direct the vote, dispose or direct the disposition of
           the Common Stock. The Reporting Persons have entered into an
           Agreement Related to the Joint Filing of Schedule 13G, dated February
           14, 2005, a copy of which is filed with this Schedule 13G as Exhibit
           A, pursuant to which the Reporting Persons have agreed to file this
           statement jointly in accordance with the provisions of Rule 13d-1(k)
           under the Act. Information with respect to each of the Reporting
           Persons is given solely by such Reporting Person, and no Reporting
           Person assumes responsibility for the accuracy or completeness of
           information provided by another Reporting Person. By their signature
           on this statement, each of the Reporting Persons agrees that this
           statement is filed on behalf of such Reporting Person. The Reporting
           Persons may be deemed to constitute a "group" for purposes of Section
           13(d)(3) of the Act. The Reporting Persons expressly disclaim that
           they have agreed to act as a group other than as described in this
           statement.

Item 2(b). Address of Principal Business Office or, if none, Residence:

           The address of the principal business office of each of the Reporting
           Persons is 222 West Adams Street, Chicago, Illinois 60606.

Item 2(c). Citizenship:

           The Fund is a Delaware limited partnership and WBCPCO is a Delaware
           limited liability company.


                               Page 6 of 10 Pages

<PAGE>

Item 2(d). Title of Class of Securities:

           Common Stock, par value $0.001 per share ("Common Stock").

Item 2(e). CUSIP No.:

           670704105

Item 3.    If this statement is filed pursuant to Rules 13d-1(b) or 13d-2(b) or
           (c), check whether the person filing is a:

           Not Applicable.

Item 4.    Ownership (as of December 31, 2004):

           As of December 31, 2004, the Fund was the registered owner Of
           2,450,594 shares of Common Stock or approximately 11.8% of the total
           number of shares of Common Stock outstanding as of such date (based
           upon information provided by the Company). The Fund has 915,217
           warrants @ $.63. By virtue of the relationship between the Fund and
           WBCPCO described in Item 2(a), WBCPCO may be deemed to possess
           indirect beneficial ownership of and shares the power to vote or
           direct the vote of the shares of Common Stock beneficially owned by
           the Fund. WBCPCO disclaims beneficial ownership of the shares of
           Common Stock owned by the Fund. The filing of this statement by
           WBCPCO shall not be construed as an admission that they are, for the
           purpose of Section 13(d) or Section 13(g) of the Act, the beneficial
           owner of any securities covered by this statement.


                               Page 7 of 10 Pages

<PAGE>

Item 5.  Ownership of Five Percent or Less of a Class:

         Not Applicable.

Item 6.  Ownership of More Than Five Percent on Behalf of Another
         Person:

         Not Applicable.

Item 7.  Identification and Classification of the Subsidiary Which
         Acquired the Security Being Reported on By the Parent Holding
         Company:

         Not Applicable.

Item 8.  Identification and Classification of Members of the Group:

         Not Applicable.

Item 9.  Notice of Dissolution of a Group:

         Not Applicable.

Item 10. Certification:

         Not Applicable.


                               Page 8 of 10 Pages

<PAGE>

                                    SIGNATURE

      After reasonable inquiry and to the best of our knowledge and belief, the
undersigned certify that the information set forth in this statement is true,
complete and correct.

Date: February 14, 2005

                                WILLIAM BLAIR CAPITAL PARTNERS VII QP, L.P.

                                By: William Blair Capital Management VII, L.P.
                                    Its: General Partner

                                By: William Blair Capital Management VII, L.L.C.
                                    Its: General Partner

                                    By: /s/ David G. Chandler
                                       ----------------------------
                                    Title: Managing Director


                                WILLIAM BLAIR CAPITAL PARTNERS VII, L.P.

                                By: William Blair Capital Management VII, L.P.
                                    Its: General Partner

                                By: William Blair Capital Management VII, L.L.C.
                                    Its: General Partner

                                    By: /s/ David G. Chandler
                                       ----------------------------
                                    Title: Managing Director


                               Page 9 of 10 Pages

<PAGE>

EXHIBIT A

                     AGREEMENT REGARDING THE JOINT FILING OF
                                  SCHEDULE 13G

                            -----------------------

William Blair Capital Partners VII QP, L.P., William Blair Capital Partners VII,
L.P., William Blair Capital Management VII, L.L.C. and William Blair Capital
Management VII, L.P. hereby agree that the Statement on Schedule 13G to which
this agreement is attached as an exhibit, as well as all future amendments to
such Statement, shall be filed jointly on behalf of each of them. This agreement
is intended to satisfy the requirements of Rule 13d-1(k) (1) (iii) under the
Securities Exchange Act of 1934, as amended.

Date: February 14, 2005

                                WILLIAM BLAIR CAPITAL PARTNERS VII QP, L.P.

                                By: William Blair Capital Management VII, L.P.
                                    Its: General Partner

                                By: William Blair Capital Management VII, L.L.C.
                                    Its: General Partner

                                    By: /s/ David G. Chandler
                                        --------------------------------
                                        Title: Managing Director


                                WILLIAM BLAIR CAPITAL PARTNERS VII, L.P.

                                By: William Blair Capital Management VII, L.P.
                                    Its: General Partner

                                By: William Blair Capital Management VII, L.L.C.
                                    Its: General Partner

                                    By: /s/ David G. Chandler
                                        --------------------------------
                                        Title: Managing Director


                               Page 10 of 10 Pages