<PAGE>

                                                                    EXHIBIT 10.6




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                            STOCK PURCHASE AGREEMENT


                                      Among


                  UNITED SURGICAL PARTNERS INTERNATIONAL, INC.

                                       and

                 THE SEVERAL PURCHASERS LISTED ON ANNEX I HERETO











                            Dated as of March 2, 1998




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<PAGE>
                                TABLE OF CONTENTS

                                                                           Page
I. PURCHASE AND SALE OF STOCK; CLOSING......................................1

      SECTION 1.01   Share Issuance, Sale and Delivery .....................1
      SECTION 1.02   Closing ...............................................2

II. REPRESENTATIONS AND WARRANTIES OF THE COMPANY...........................2

      SECTION 2.01   Organization, Qualifications and Corporate Power.......2
      SECTION 2.02   Authorization of Agreements, Etc.......................2
      SECTION 2.03   Validity...............................................3
      SECTION 2.04   Authorized Capital Stock...............................3
      SECTION 2.05   Governmental Approvals.................................3
      SECTION 2.06   Corporate Transactions.................................4

III. REPRESENTATIONS AND WARRANTIES OF THE PURCHASERS.......................4

      SECTION 3.01   Authorization..........................................4
      SECTION 3.02   Validity...............................................4
      SECTION 3.03   Investment Representations ............................5

IV. CONDITIONS PRECEDENT....................................................6

      SECTION 4.01   Conditions Precedent to the
                     Obligations of the Purchasers..........................6
      SECTION 4.02   Conditions Precedent to the
                     Obligations of the Company.............................6

V. MISCELLANEOUS ...........................................................7

      SECTION 5.01   Expenses, Etc..........................................7
      SECTION 5.02   Survival of Agreements.................................7
      SECTION 5.03   Parties in Interest....................................7
      SECTION 5.04   Notices................................................8
      SECTION 5.05   Entire Agreement; Modifications........................8
      SECTION 5.06   Counterparts...........................................8
      SECTION 5.07   Assignment.............................................8
      SECTION 5.08   Governing Law..........................................9

TESTIMONIUM................................................................10
<PAGE>
                          INDEX TO EXHIBITS AND ANNEXES



      EXHIBIT                 DESCRIPTION

        A                     Form of Registration Rights Agreement
        B                     Form of Stockholders Agreement

      ANNEX                   DESCRIPTION

        I                     Purchasers

                                       ii
<PAGE>
      STOCK PURCHASE AGREEMENT, dated as of March 2, 1998, among UNITED SURGICAL
PARTNERS INTERNATIONAL, INC., a Delaware corporation (the "Company") and the
several purchasers listed on Annex I hereto (hereinafter referred to
individually as a "Purchaser" and collectively as the "Purchasers").

      WHEREAS, subject to the terms and conditions set forth herein, the Company
wishes to issue, sell and deliver to the Purchasers an aggregate 500,000 shares
of Class A Common Stock, $.01 par value ("Class A Common Stock"), of the
Company;

      WHEREAS, the Purchasers, severally and not jointly, wish to purchase such
shares of Class A Common Stock, all on the terms subject to the conditions
hereinafter set forth;

      WHEREAS, in order to induce the Purchasers to consummate the transactions
contemplated by this Agreement, the Company has agreed to grant to the
Purchasers certain registration rights with respect to the shares of Class A
Common Stock purchased by them hereunder pursuant to a Registration Rights
Agreement substantially in the form attached hereto as Exhibit A (the
"Registration Rights Agreement"); and

      NOW, THEREFORE, in consideration of the premises and the mutual covenants
herein contained, the parties hereto agree as follows:



                                       I.

                           PURCHASE AND SALE OF STOCK

      SECTION 1.01 ISSUANCE, SALE AND DELIVERV OF THE SHARES.

      (a) Subject to the terms and conditions set forth herein, the Company
shall issue, sell and deliver to each Purchaser, and each Purchaser shall
purchase from the Company, on the Closing Date (as hereinafter defined), the
number of shares of Class A Common Stock appearing opposite the name of such
Purchaser on Annex I hereto under the heading "Class A Common Shares"
(collectively, the "Shares"). On the Closing Date, the Company shall issue
certificates in definitive form to each Purchaser, registered in the name of
such Purchaser, evidencing the Shares being purchased by it hereunder.

      (b) As payment in full for the Shares being purchased by it hereunder, and
against delivery thereof as aforesaid on the Closing Date, each Purchaser shall
pay to the Company, by wire transfer of immediately available funds, to an
account designated by the Company, the amount appearing opposite the name of
such Purchaser on Annex I hereto under the heading "Purchase Price."

<PAGE>
      SECTION 1.02 CLOSING. The closing of the sale and purchase of the Shares
shall take place at the offices of Reboul, MacMurray, Hewitt, Maynard & Kristol,
45 Rockefeller Plaza, New York, New York 10111, at 10 a.m., New York time, on
March 2, 1998, or at such other date and time as may be mutually agreed upon by
the Purchasers and the Company (such date and time of the closing being herein
called the "Closing Date").


                                       II.

                  REPRESENTATIONS AND WARRANTIES OF THE COMPANY

      The Company represents and warrants to the Purchasers as follows:

      SECTION 2.01 ORGANIZATION, QUALIFICATIONS AND CORPORATE POWER. The Company
is a corporation duly incorporated, validly existing and in good standing under
the laws of the State of Delaware and is duly licensed or qualified in each
jurisdiction in which the nature of its business or the ownership of its
properties makes such licensing or qualification necessary, except where the
failure to be so licensed or qualified would not have a material adverse effect
on its ability to carry on its business. The Company has the corporate power and
authority to own and hold its properties, to carry on its business as currently
conducted and to execute and deliver this Agreement, the Stockholders Agreement
substantially in the form attached hereto as Exhibit B (the "Stockholders
Agreement") and the Registration Rights Agreement, to perform its obligations
under this Agreement, the Stockholders Agreement and the Registration Rights
Agreement and to issue and deliver the Shares.

      SECTION 2.02 AUTHORIZATION OF AGREEMENTS, ETC.

      (a) Each of the execution and delivery by the Company of this Agreement,
the Stockholders Agreement and the Registration Rights Agreement, the
performance by the Company of its obligations hereunder and under the
Stockholders Agreement and the Registration Rights Agreement, and the issuance
and sale by the Company of the Shares have been duly authorized by all requisite
corporate action and will not violate any provision of law, any order of any
court or other agency of government, the Certificate of Incorporation or By-laws
of the Company, or any provision of any indenture, agreement or other instrument
to which the Company or any of the properties or assets of the Company is bound,
or conflict with, result in a breach of or constitute (with due notice or lapse
of time or both) a default under any such indenture, agreement or other
instrument, or result in the creation or imposition of any lien, charge or

                                       2
<PAGE>
encumbrance of any nature whatsoever upon any of the properties or assets of the
Company.

      (b) The Shares have been duly authorized by the Company and, when sold and
paid for in accordance with this Agreement, will be validly issued, fully paid
and nonassessable shares of Class A Common Stock. The issuance, sale and
delivery of the Shares to the Purchasers hereunder is not subject to any
preemptive rights of stockholders of the Company or to any right of first
refusal or other similar right in favor of any person.

      SECTION 2.03 VALIDITY. This Agreement has been duly executed and delivered
by the Company and constitutes the legal, valid and binding obligation of the
Company, enforceable against the Company in accordance with its terms, subject,
as to enforcement of remedies, to applicable bankruptcy, insolvency,
reorganization, moratorium and similar laws from time to time in effect
affecting the enforcement of creditors' rights generally and to general equity
principles. The Stockholders Agreement and the Registration Rights Agreement,
when executed and delivered by the Company as provided in this Agreement, and
when executed and delivered by the other parties hereto, will constitute the
legal, valid and binding obligations of the Company, enforceable against the
Company in accordance with their respective terms, subject, as to enforcement of
remedies, to applicable bankruptcy, insolvency, reorganization, moratorium and
similar laws from time to time in effect affecting the enforcement of creditors'
rights generally and to general equity principles.

      SECTION 2.04 AUTHORIZED CAPITAL STOCKS

      (a) The authorized capital stock of the Company consists of 25,000,000
shares of Common Stock, $.01 par value and 20,000,000 shares of Class A Common
Stock. No shares of capital stock of the Company have ever been issued.

      (b) Except as contemplated by this Agreement, (i) no subscription,
warrant, option, convertible security or other right (contingent or other) to
purchase or acquire any shares of any class of capital stock of the Company is
authorized or outstanding, (ii) there is no binding commitment of the Company to
issue any shares, warrants, options or other such rights or to distribute to
holders of any class of the Company's capital stock, any evidences of
indebtedness or assets, and (iii) the Company has no obligations (contingent or
other) to purchase, redeem or otherwise acquire any shares of its capital stock
or any interest therein or to pay any dividend or make any other distribution in
respect thereof.

      SECTION 2.05 GOVERNMENTAL APPROVALS. Subject to the accuracy of the
representations and warranties of the Purchasers set forth in Article III
hereof, no registration or filing with,

                                       3
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or consent or approval of, or other action by, any Federal, state or other
governmental agency or instrumentality is or will be necessary for the valid
execution and delivery of this Agreement, the Stockholders Agreement and the
Registration Rights Agreement, the performance of this Agreement, the
Stockholders Agreement and the Registration Rights Agreement, or the issuance,
sale and delivery of the Shares.

      SECTION 2.06 CORPORATE TRANSACTIONS. The Company was incorporated on
February 27, 1998. Since such date of incorporation, the Company has not
conducted any business or otherwise entered into any transactions other than (x)
its organization, the adoption of its By-laws and the election of directors and
officers and (y) the authorization of this Agreement, the Stockholders Agreement
and the Registration Rights Agreement.


                                      III.

                REPRESENTATIONS AND WARRANTIES OF THE PURCHASERS

      Each Purchaser represents and warrants to the Company, severally and not
jointly, as follows:

      SECTION 3.01 AUTHORIZATION. The execution, delivery and performance by
such Purchaser of this Agreement, the Stockholders Agreement and the
Registration Rights Agreement, and the purchase and receipt by such Purchaser of
the Shares being purchased by it hereunder have been duly authorized by all
requisite action on the part of such Purchaser, and will not violate any
provision of law, any order of any court or other agency of government
applicable to such Purchaser, the governing instrument of such Purchaser, or any
provision of any indenture, agreement or other instrument by which such
Purchaser or any of such Purchaser's properties or assets are bound, or conflict
with, result in a breach of or constitute (with due notice or lapse of time or
both) a default under any such indenture, agreement or other instrument.

      SECTION 3.02 VALIDITY. This Agreement has been duly executed and delivered
by such Purchaser and constitutes the legal, valid and binding obligation of
such Purchaser, enforceable against such Purchaser in accordance with its terms,
subject, as to enforcement of remedies, to applicable bankruptcy, insolvency,
reorganization, moratorium and similar laws from time to time in effect
affecting the enforcement of creditors' rights generally and to general equity
principles. The Stockholders Agreement and the Registration Rights Agreement,
when executed and delivered by such Purchaser in accordance with this Agreement,
and when executed and delivered by the other parties hereto, will constitute the
legal, valid and binding obligation

                                       4
<PAGE>
of such Purchaser, enforceable in accordance with their terms, subject, as to
enforcement of remedies, to applicable bankruptcy, insolvency, reorganization,
moratorium and similar laws from time to time in effect affecting the
enforcement of creditors' rights generally and to general equity principles.

      SECTION 3.03 INVESTMENT REPRESENTATIONS.

      (a) Such Purchaser is acquiring the Shares for its own account, for
investment, and not with a view toward the resale or distribution thereof in
violation of applicable law.

      (b) Such Purchaser understands that it must bear the economic risk of its
investment for an indefinite period of time because the Shares are not
registered under the Securities Act of 1933, as amended (the "Securities Act")
or any applicable state securities laws, and may not be resold unless
subsequently registered under the Securities Act and such other laws or unless
an exemption from such registration is available. Such Purchaser also
understands that, except as provided in the Registration Rights Agreement, it is
not contemplated that any registration will be made under the Securities Act of
1933, as amended (the "Securities Act") or that the Company will take steps
which will make the provisions of Rule 144 under the Securities Act available to
permit resale of the Shares. Such Purchaser will not pledge, transfer, convey or
otherwise dispose of any of the Shares, except (i) in connection with a
distribution to its partners, or (ii) in a transaction that is the subject of
either (x) an effective registration statement under the Securities Act and any
applicable state securities laws, or (y) an opinion of counsel to the effect
that such registration is not required (which opinion and counsel shall be
reasonably satisfactory to the Company, it being agreed that Reboul, MacMurray,
Hewitt, Maynard & Kristol shall be satisfactory, and may be relied on by the
Company in making such determination), it being intended that the agreements
with respect to the Shares contained in this sentence shall be construed
consistently with the provisions relating to the same subject matter contained
in the Registration Rights Agreement.

      (c) Such Purchaser is able to fend for itself in the transactions
contemplated by this Agreement and has the ability to bear the economic risks of
its investment in the Shares being purchased by it for an indefinite period of
time. Such Purchaser has had the opportunity to ask questions of, and receive
answers from, officers of the Company with respect to the business and financial
condition of the Company and the terms and conditions of the offering of the
Shares and to obtain additional information necessary to verify such information
or can acquire it without unreasonable effort or expense.

                                       5
<PAGE>
      (d) Such Purchaser has such knowledge and experience in financial and
business matters that it is capable of evaluating the merits and risks of its
investment in the Shares. Such Purchaser is an "accredited investor" as such
term is defined in Rule 501 of Regulation D under the Securities Act with
respect to its purchase of the Shares, and that if such Purchaser is a
partnership, it has not been formed solely for the purpose of purchasing the
Shares it is purchasing hereunder.


                                       IV.

                              CONDITIONS PRECEDENT

      SECTION 4.01 CONDITIONS PRECEDENT TO THE OBLIGATIONS OF THE PURCHASERS.
The obligations of each Purchaser hereunder are, at its option, subject to the
satisfaction, on or before the Closing Date, of the following conditions:

      (a) REPRESENTATIONS AND WARRANTIES TO BE TRUE AND CORRECT. The
representations and warranties of the Company contained in this Agreement shall
be true and correct in all material respects on the Closing Date, with the same
force and effect as though such representations and warranties had been made on
and as of such date.

      (b) PERFORMANCE. The Company shall have performed and complied with all
agreements and conditions contained herein required to be performed or complied
with by it prior to or on the Closing Date.

      (c) ALL PROCEEDINGS TO BE SATISFACTORY. All corporate and other
proceedings to be taken by the Company and all waivers and consents to be
obtained by the Company in connection with the transactions contemplated hereby
shall have been taken or obtained by the Company and all documents incident
thereto shall be satisfactory in form and substance to such Purchaser and its
counsel.

      (d) STOCKHOLDERS AGREEMENT AND REGISTRATION RIGHTS AGREEMENT. The Company
shall have executed and delivered the Stockholders Agreement and the
Registration Rights Agreement.

      SECTION 4.02 CONDITIONS PRECEDENT TO THE OBLIGATIONS OF THE COMPANY. The
obligations of the Company hereunder are, at its option, subject to the
satisfaction, on or before the Closing Date of the following conditions:

      (a) REPRESENTATIONS AND WARRANTIES TO BE TRUE AND CORRECT. The
representations and warranties of the Purchasers contained in this Agreement
shall be true and correct in all material respects on the Closing Date, with the
same effect as

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<PAGE>
though such representations and warranties had been made on and as of such date.

      (b) PERFORMANCE. The Purchasers shall have performed and complied with all
agreements and conditions contained herein required to be performed or complied
with by them prior to or on the Closing Date.

      (c) ALL PROCEEDINGS TO BE SATISFACTORY. All proceedings to be taken by the
Purchasers and any waivers and consents to be obtained by the Purchasers in
connection with the transactions contemplated hereby shall have been taken or
obtained by the Purchasers and all documents incident thereto shall be
satisfactory in form and substance to the Company and its counsel.

      (d) STOCKHOLDERS AGREEMENT AND REGISTRATION RIGHTS AGREEMENT. The
Purchasers shall have executed and delivered the Stockholders Agreement and the
Registration Rights Agreement.


                                       V.

                                  MISCELLANEOUS

      SECTION 5.01 EXPENSES, ETC. The Company shall pay its own expenses. All
fees and expenses of the Purchasers incident to the negotiation, preparation and
execution of this Agreement, including the fees and expenses of counsel,
accountants or other advisors (i) shall be paid by the Company in the event that
such transactions are consummated and (ii) shall be borne by the party incurring
such expense in the event such transactions are not consummated. Each party
hereto will indemnify and hold harmless the others against and in respect of any
claim for brokerage or other commissions relative to this Agreement or to the
transactions contemplated hereby, made as a result of any agreements,
arrangements or understandings made or claimed to have been made by such party
with any third party.

      SECTION 5.02 SURVIVAL OF AGREEMENTS. All covenants, agreements,
representations and warranties made herein shall survive the execution and
delivery of this Agreement and the issuance, sale and delivery of the Shares
pursuant hereto and all statements contained in any certificate or other
instrument delivered by the Company hereunder shall be deemed to constitute
representations and warranties made by the Company.

      SECTION 5.03 PARTIES IN INTEREST. All covenants and agreements contained
in this Agreement by or on behalf of any of the parties hereto shall bind and
inure to the benefit of the respective successors and assigns of the parties
hereto whether so expressed or not.

                                       7
<PAGE>
      SECTION 5.04 NOTICES. Any notice or other communications required or
permitted hereunder shall be deemed to be sufficient if contained in a written
instrument delivered in person or by overnight courier or duly sent by first
class certified mail, postage prepaid, or by facsimile addressed to such party
at the address or facsimile number set forth below:

      if to the Company, to:


            United Surgical Partners International, Inc.
            5151 Belt Line Road
            Suite 605
            Dallas, Texas 75240
            Facsimile: 972-385-7351
            Attention: Donald Steen

if to any other Purchaser to such Purchaser at the address appearing on Annex I
hereto;

            with a copy to:

            Reboul, MacMurray, Hewitt, Maynard & Kristol
            45 Rockefeller Plaza
            New York, New York 101l1
            Facsimile: (212) 841-5785
            Attention: Othon Prounis, Esq.

or, in any case, at such other address or addresses as shall have been furnished
in writing by such party to the other parties hereto. All such notices,
requests, consents and other communications shall be deemed to have been
received (a) in the case of personal or courier delivery, on the date of such
delivery, (b) in the case of mailing, on the fifth business day following the
date of such mailing and (c) in the case of facsimile, when received.

      SECTION 5.05 ENTIRE AGREEMENT; MODIFICATIONS. This Agreement, the
Stockholders Agreement and the Registration Rights Agreement constitute the
entire agreement of the parties with respect to the subject matter hereof and
may not be amended or modified nor any provisions waived except in a writing
signed by the party to be charged.

      SECTION 5.06 COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

      SECTION 5.07 ASSIGNMENT. This Agreement may not be assigned by any party
without the prior written consent of the others.

                                       8
<PAGE>
      SECTION 5.08 GOVERNING LAW. This Agreement shall be governed by and
construed in accordance with the laws of the State of New York.

                                       9
<PAGE>
      IN WITNESS WHEREOF, the Company and the Purchasers have executed this
Agreement as of the day and year first above written.


                                          UNITED SURGICAL PARTNERS
                                          INTERNATIONAL, INC.

                                          By /s/ DONALD STEEN
                                          Name:  Donald Steen
                                          Title: Chairman & CEO


                                          PURCHASERS:

                                          WELSH, CARSON, ANDERSON
                                          & STOWE VII, L.P.

                                          By: WCAS VII Partners, L.P.
                                          General Partner

                                          By /s/ LAURA VANBUREN
                                          Name:  Laura VanBuren
                                          Title: General Partner


                                          WCAS HEALTHCARE PARTNERS, L.P.

                                          By: WCAS HC Partners
                                          General Partner

                                          By /s/ RUSSELL L. CARSON
                                          Name:  Russell L. Carson
                                          Title: General Partner
<PAGE>
                                          Patrick J. Welsh
                                          Russell L. Carson
                                          Bruce K. Anderson
                                          Richard H. Stowe
                                          Andrew M. Paul
                                          Thomas E. McInerney
                                          Robert A. Minicucci
                                          Anthony J. deNicola
                                          Paul B. Queally


                                          /s/ LAURA VANBUREN
                                          By  Laura VanBuren
                                          Attorney-in-Fact


                                          /s/ LAURA VANBUREN
                                              Laura VanBuren


                                          /s/ RUDOLPH E. RUPERT
                                              Rudolph E. Rupert


                                          /s/ D. SCOTT MACKESY
                                              D. Scott Mackesy


                                          /s/ DONALD STEEN
                                              Donald Steen

<PAGE>

                              ANNEX I - PURCHASERS

                                                     Class A          Purchase
                                                     Common Shares    Price
                                                     -------------    --------

Welsh, Carson Anderson
  & Stowe VII, L.P.                                  415,391          $  830,782
WCAS Healthcare Partners, L.P.                         6,208              12,416
Patrick J. Welsh                                       5,064              10,128
Russell L. Carson                                      5,064              10,128
Bruce K. Anderson                                      5,064              10,128
Richard H. Stowe                                         887               1,774
Andrew M. Paul                                           887               1,774
Thomas E. McInerney                                    2,661               5,322
Laura VanBuren                                            45                  90
Robert A. Minicucci                                      887               1,774
Anthony deNicola                                         310                 620
Rudolph E. Rupert                                        133                 266
Paul B. Queally                                          683               1,366
D. Scott Mackesy                                         177                 354

c/o Welsh, Carson, Anderson
  & Stowe
320 Park Avenue
Suite 2500
New York, NY 10022-9500

Donald Steen                                          56,539          $  113,078

c/o United Surgical Partners
   International, Inc.
5151 Belt Line Road
Suite 605
Dallas, Texas 75240
Facsimile: 972-385-7351
                            Total:                   500,000          $1,000,000