<PAGE>   1
                                                                   EXHIBIT 10.23

                  SECOND MODIFICATION AND RATIFICATION OF LEASE

        THIS SECOND MODIFICATION AND RATIFICATION OF LEASE ("Modification") is
made and entered into effective this ___ day of December 1999 by and between ST.
PAUL PROPERTIES, INC., a Delaware corporation ("Landlord"), and THE TRIZETTO
GROUP, INC., a Delaware corporation ("Tenant").

                                  WITNESSETH:

        WHEREAS, Landlord and Tenant entered into that certain Office Lease
dated as of April 26, 1999, as amended by that certain Lease commencement letter
signed by Landlord on September 9, 1999, and by Tenant on September 7, 1999, and
by that certain First Modification and Ratification of Lease entered into
effective November 1, 1999 (hereafter collectively the "Lease"), for the rental
of certain commercial real property located in the Building known as Atrium I,
6061 S. Willow Drive, Englewood, Colorado, and more particularly described in
the Lease as Suite 310 (the "Premises"); and

        WHEREAS, effective May 1, 2000, Tenant desires to expand the Premises
through the addition of Suite 300 in the Building, containing approximately
22,670 rentable square feet on the third floor of the Building (the "Expansion
Premises") as depicted in Exhibit A-1; and

        WHEREAS, Tenant desires to extend the term of the Lease for the primary
Premises to be coterminous with the term of the Lease for the Expansion Premises
as set forth below; and

        WHEREAS, Landlord is willing to modify the Lease to accommodate such
desires, subject to the terms and conditions of this Modification and Landlord
and Tenant desire to amend the Lease to reflect the addition of the Expansion
Premises, the extension of the Lease Term and the increase in Base Rent payable
under the Lease.

        NOW, THEREFORE, in consideration of the foregoing, the agreements of the
parties, and other good and valuable consideration, the receipt and sufficiency
of which is hereby acknowledged, the parties agree as follows:

        1. Definitions. All capitalized terms used herein not otherwise defined
in this Modification shall have the meanings given them in the Lease.

        2. Additional Premises. Effective May 1, 2000, or upon substantial
completion of the tenant improvements to be made to the Expansion Premises as
defined in Exhibit B-1 attached hereto, whichever is later ("Expansion Premises
Commencement Date"), Landlord shall lease to Tenant and Tenant shall lease from
Landlord the Expansion Premises. It is expressly understood that the actual
number of rentable square feet within the Expansion Premises is subject to
confirmation in accordance with BOMA standards based upon the final space plan
to be prepared by Landlord's architect for the Expansion Premises, and the
parties agree to further amend the Lease to reflect any change in the actual
size of the Expansion Premises,



<PAGE>   2

together with the calculation of Base Rent, and all other matters that are
dependent upon the size of the Expansion Premises. In addition the
identification of the Leased Premises in Section 1.03 (B) of the Lease is hereby
amended by adding immediately after the description of the Leased Premises the
following:

        EXPANSION PREMISES:

                  That part of the Building outlined on Exhibit A-1, called
                  Suite 300, on the third floor(s) of the Building, containing
                  approximately 22,670 rentable square feet, including tenant
                  improvements to be made by Landlord pursuant to Exhibit B-1 to
                  the Second Modification and Ratification of Lease.

        3. Expansion Premises Commencement Date. Section 1.03(D) of the Lease is
hereby amended by adding immediately after the description of the commencement
date of the Lease the following:

                  The Expansion Premises Commencement Date shall be May 1, 2000,
                  unless delayed by Force Majeure, or as otherwise delayed as
                  provided in Exhibit "B1 " to the Second Modification and
                  Ratification of Lease.

        4. Expansion Premises Completion Date. Section 1.03(E) of the Lease is
hereby amended by adding immediately after the description of the completion
date under the Lease the following:

                  The Expansion Premises Completion Date shall be May 1, 2000,
                  unless delayed by Force Majeure, or as otherwise delayed as
                  provided in Exhibit "B-1" to the Second Modification and
                  Ratification of Lease.

        5. Termination Date. Section 1.03(F) of the Lease is hereby amended in
its entirety by replacing the existing Termination Date of the Lease of November
30, 2004, with the following:

                  The Termination Date of the Lease for the Premises and the
                  Expansion Premises shall be April 30, 2006 (seventy-two (72)
                  months following the Expansion Premises Commencement Date),
                  unless sooner terminated as provided in this Lease, or as
                  otherwise extended as provided in Exhibit "B-1" to the Second
                  Modification and Ratification of Lease.

        6. Expansion Premises Term. Section 1.03(G) of the Lease is hereby
amended by adding immediately after the description of the Term of the Lease the
following:

                  The Term of the Lease for the Premises shall be extended so
                  that it coincides with the expiration of the Term for the
                  Expansion Premises. The Expansion Premises Term shall be a
                  period of seventy-two (72) months commencing on the Expansion
                  Premises Commencement Date and expiring at 11:59 p.m. local
                  time



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<PAGE>   3

                  on the Termination Date, unless sooner terminated or extended
                  as provided in this Lease.

        7. Tenant's Proportionate Share. Section 1.03(J) of the Lease is amended
effective on the Expansion Premises Commencement Date by adding immediately
after the description of the Tenant's Proportionate Share under the Lease for
the Premises the following:

                  Tenant's Proportionate Share for the Expansion Premises shall
                  be 17.52%.

        8. Security Deposit. Section 1.03(K) of the Lease is hereby amended by
increasing the security deposit for the Premises and Expansion Premises in the
amount of Thirty-seven Thousand Three Hundred Eleven and 04/100 Dollars
($37,311.04), for a total security deposit of One Hundred Fifteen Thousand
Twenty-seven and 29/100 Dollars ($115,027.29), which additional amount shall be
payable to Landlord upon execution of this Modification.

        9. Parking Spaces. Section 1.03(O) of the Lease is amended effective on
the Expansion Premises Commencement Date by the addition of the following at the
end of the section:

                  During the Expansion Premises Term, Tenant shall be entitled
                  to the additional non-exclusive use in common with Landlord
                  and others of a maximum of seventy-four (74) parking spaces in
                  the Building parking areas at no charge during the primary
                  Term of the Lease. Within the foregoing parking allowance,
                  Tenant shall be entitled during the primary Lease Term to ten
                  (10) covered parking spaces in the Building parking area at
                  the rate of $30.00 per parking space per month. In addition,
                  through June 30, 2002, Tenant may be entitled to use
                  additional parking spaces, in an amount to be determined by
                  Landlord, on a non-reserved, non-exclusive basis in common
                  with other tenants of the Building, in that certain parking
                  lot adjacent to the Building parking lot and currently leased
                  by Landlord and known as the "Sheplers" parking lot, at no
                  additional cost to Tenant. Landlord reserves the right to
                  strictly enforce the number of parking spaces utilized by
                  Tenant during the term of this Lease based upon a parking
                  ratio of 3.3 parking spaces per 1,000 rentable square feet.

        10. Operating Expenses. Section 2.02 of the Lease shall be amended
effective on the Expansion Premises Commencement Date by adding to the first
sentence thereof immediately after the words "the 1999 base year" and
immediately before the parenthetical reference "("Excess Expenses")," the
following:

                  for the Premises through November 30, 2004, and during the
                  2000 base year with respect to the Expansion Premises during
                  the Expansion Premises Term and with respect to the Premises
                  beginning on December 1, 2004.

        In addition, the following shall be added immediately after the last
paragraph of Section 2.02:

                  If during any calendar year of this Lease, the occupancy of
                  the Building averages less than ninety-five percent (95%),
                  it is agreed that the Operating Expenses with



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                  respect to the Expansion Premises shall be computed as though
                  the Building had been ninety-five percent (95%) occupied for
                  such calendar year.

        11. Base Rent. Effective on the Expansion Premises Commencement Date,
Section 1.03(H) of the Lease entitled Base Rent, and Section 1.03(I) of the
Lease entitled Monthly Installments of Base Rent, shall be amended in their
entirety and replaced with the following:

                  (a)  Base Rent. Tenant shall pay Base Rent for the Premises,
                       payable monthly in advance, without demand, deduction or
                       set-off, in accordance with the following schedule:

<TABLE>
<CAPTION>
                           Rentable           Lease            Annual              Monthly
      Months              Square Feet         Rate             Payment             Payment
      ------              -----------         ----             -------             -------
<S>                       <C>              <C>               <C>                 <C>
       1-61                 23,610         $21.04/rsf        $496,754.40         $41,396.20
(11/8/99-11/30/2004)
        62-73               23,610         $21.46/rsf        $506,670.60         $42,222.55
(12/1/2004-11/30/2005)
        74-78               23,610         $21.89/rsf        $516,822.90         $43,068.58
(12/1/2005-4/30/2006)
</TABLE>

                  (b)  Expansion Premises Base Rent. In addition to the Base
                       Rent payable with respect to the Premises, Tenant shall
                       also pay Base Rent with respect to the Expansion
                       Premises, payable monthly in advance, without demand,
                       deduction or set-off, in accordance with the following
                       schedule:

<TABLE>
<CAPTION>
                        Rentable           Lease              Annual               Monthly
      Months           Square Feet         Rate               Payment              Payment
      ------           -----------         ----               -------              -------
<S>                    <C>              <C>                 <C>                  <C>
       1-60              22,670         $19.75/rsf          $447,732.50          $37,311.04
 (5/1/00-4/30/05)
       61-72             22,670         $20.15/rsf          $456,800.50          $38,066.71
 (5/1/05-4/30/06)
</TABLE>

        12. Termination Option. Paragraph 3 of the Addendum to the Lease shall
be deleted in its entirety and replaced with the following:

        Provided no Event of Default has occurred and is continuing, and
        provided that Tenant has not assigned the Lease or sublet all or any
        portion of the Premises or the Expansion Premises, and in the event
        Landlord is unable to accommodate within the Building the growth
        requirements of Tenant, Tenant shall have the option, in its sole
        discretion, to terminate the Lease with respect to the Premises and the
        Expansion Premises on April



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        30, 2005, by providing Landlord with one-hundred eighty (180) days'
        prior written notice of Tenant's intent to terminate the Lease with
        respect to the Expansion Premises, and provided that by April 30, 2005,
        Tenant shall pay Landlord a termination fee equal to the sum of all of
        Landlord's unamortized costs of leasing the Premises and Expansion
        Premises to Tenant, including but not limited to leasing commissions,
        tenant improvements and other concessions, plus an amount equal to four
        (4) months of the then existing Base Rent for the Premises and Expansion
        Premises.

13. Tenant Improvements. Landlord agrees to provide Tenant with an allowance for
tenant improvements for the Expansion Premises in the amount and in the manner
as set forth in the attached Exhibit B-1 - Provisions Relating To Construction
Of Tenant's Expansion Premises (Finish Allowance only).

14. Right of Offer. Paragraph 2 of the Addendum to the Lease shall be deleted in
its entirety and replaced with the following:

        During the initial Term of the Lease, Tenant shall have a right of
        offer, subject to existing rights granted to other tenants as of the
        date of this Modification, to lease any space that may become vacant and
        located on the second (2nd) floor of the Building as more particularly
        shown on Exhibit A-2 attached hereto (the "Offer Space"), if and when
        the Offer Space becomes "available for lease." For purposes of this
        right of offer, the Offer Space will be considered to be "available for
        lease" if (i) no bona fide written lease agreement is currently in force
        or effect with respect to such space, (ii) the space becomes vacant, or
        will become vacant, because an existing tenant's lease has or will
        expire or be terminated with no renewal or extension options subject to
        being exercised with respect to such space, and (iii) Landlord makes the
        Offer Space available for leasing to others. Tenant's right of offer
        with respect to such Offer Space shall be upon the following terms and
        conditions:

        a)   In the event that (i) the Offer Space, or any part thereof, becomes
             or is about to become available for lease as provided above,
             Landlord will notify Tenant of the rental terms on which it would
             be willing to lease the Offer Space to Tenant, and Tenant shall
             have a right of offer to lease that portion of the Offer Space
             identified in Landlord's notice, subject to existing rights granted
             to other tenants as of the date of this Modification, at the rent
             and on the terms and conditions contained in Landlord's notice.

        b)   The right of offer will be exercised by Tenant signing a lease
             amendment with respect to the subject portion of the Offer Space at
             the rent and on the terms set forth in Landlord's notice. Tenant
             shall accept or reject the offer contained in Landlord's notice
             within five business (5) days after the receipt of Landlord's
             notice. If an amendment incorporating the terms contained in
             Landlord's notice is not signed within five business (5) days
             following receipt of Landlord's notice, time being strictly of the
             essence, Landlord will have the right to lease all or a portion of
             the Offer Space free of the rights of Tenant under this



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             Paragraph, and Tenant's right of offer granted herein shall be null
             and void. Any space leased by Tenant will be added to the Premises
             as of the date provided in the proposed amendment.

        c)   Landlord is under no obligation to offer for lease all or any
             portion of the Offer Space to Tenant or any other person.

        d)   Notwithstanding any other provision set forth above, it is agreed
             that Tenant shall not be permitted to exercise any of its rights
             contained in this Paragraph 14 at any time when the Lease is not in
             effect or at any time when an Event of Default exists, (ii) in the
             event that Tenant assigns the Lease or sublets any portion of the
             Premises or the Expansion Premises at any time, and (iii) Tenant
             may not exercise the right contained in this Paragraph 14 if the
             effective date of the addition of the Offer Space to the Premises
             previously leased would be at any time during the last year of the
             then existing term of the Lease.

        e)   In the event that Tenant fails to exercise the foregoing right of
             offer as provided in this Paragraph 14, time being strictly of the
             essence, Tenant's right of offer shall be null and void.

        f)   Tenant acknowledges that it is only being granted a right of offer
             that is subject and subordinate to the rights of any existing
             tenant with pre-existing rights of refusal, rights of offer, or
             options to lease, as of the date of this Modification.

        g)   In no event shall Landlord be responsible for any brokerage
             commission for any real estate broker retained by Tenant with
             respect to this right of first offer.

        15. Monument Signage. Provided that Tenant is not then in default of the
Lease, and provided that Tenant has not assigned this Lease, nor sublet all or
any portion of the Premises or the Expansion Premises, Landlord shall permit
Tenant to utilize the Building monument signage located on the east side or west
side of the Building, but not both. All signage plans shall be subject to
Landlord's approval, and further shall comply with all laws governing use of
such signage, including but not limited to the those restrictions imposed by the
Denver Technological Center Architectural Control Committee and the City of
Greenwood Village, Colorado. Tenant, at its sole cost and expense, shall be
responsible for costs related to such monument signage.

        16. Real Estate Brokers. Each of the parties hereto hereby warrants and
represents to the other party that it has not dealt with or been represented by
any broker in connection with its execution of this Modification other than
Landlord's listing agent, Venture Group Real Estate, LLC, acting as agent of
Landlord, and Julien J. Studley, Inc., acting as agent-of Tenant. Landlord shall
be responsible for payment of any compensation or commission to Venture Group
Real Estate, LLC, and Julien J. Studley, Inc., with respect to this
Modification. Tenant agrees to indemnify and hold Landlord harmless from and
against any other claims for commissions or similar compensation from any other
person claiming an entitlement to any such payment as a result of its
representation of Tenant. In addition, Landlord agrees to indemnify and hold
Tenant harmless from and against any claims for commissions or similar



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compensation from any other broker or person claiming an entitlement to any such
payment as a result of its representation of Landlord.

        17. Performance of Obligations. Tenant hereby acknowledges and confirms
that, as of the date hereof, Landlord has performed all obligations on the part
of the Landlord under the Lease and that Tenant has no claims against Landlord
or claims of offset against any rent or other sums payable by Tenant under the
Lease.

        18. Conflicts and Non-Amended Provisions. In the event of any express
conflict or inconsistency between the terms of the Lease and the terms of this
Modification, the terms of this Modification shall control and govern. In all
other respects, the terms, covenants and conditions of the Lease are hereby
ratified, reaffirmed and republished in their entirety.

        19. Condition Precedent. This Modification, and Tenant's right to lease
the Expansion Space, is expressly conditioned upon the Expansion Premises being
available to lease, and is subject to pre-existing rights of existing tenants in
the Building. In the event that any tenants within the Building exercise any
pre-existing rights to the Expansion Space, time being strictly of the essence,
this Modification shall be null and void.

        20. No Offer. The submission of this Modification by Landlord to the
Tenant is not an offer to modify or amend the Lease and is not effective until
execution and delivery by both Landlord and Tenant.

        21. Entire Agreement. This Modification contains the entire agreement
between the parties as to its subject matter and supersedes any and all prior
agreements, arrangements or understandings between the parties relating to the
subject matter hereof.

        22. Counterparts. This Modification may be executed in a number of
identical counterparts, each of which shall be deemed an original for all
purposes, but all of which together shall constitute one and the same
instrument.

        IN WITNESS WHEREOF, the parties have entered into this Modification
effective as of the date first set forth hereinabove.

LANDLORD:                                  TENANT:

ST. PAUL PROPERTIES, INC., a               THE TRIZETTO GROUP, INC.,
Delaware corporation                       a Delaware corporation


By: /s/ R. WILLIAM INSERRA           By:  /s/   MJ SUNDERLAND
   -----------------------------     -----------------------------------
      R. William Inserra             Name:  MJ SUNDERLAND
      Vice President -               Title: SR VP, CFO
      Asset Management





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                                  EXHIBIT "B-1"
            PROVISIONS RELATING TO CONSTRUCTION OF TENANT'S EXPANSION
                                    PREMISES
                            (FINISH ALLOWANCE ONLY)

        1. Landlord will provide Tenant with a construction credit in the sum of
up to Fifteen and No/100 Dollars ($15.00) per rentable square foot of the
Expansion Premises, which equals Three Hundred Forty Thousand Fifty and No/100
Dollars ($340,050.00) (the "Construction Credit"), which may be used only
against the cost of design and construction by Landlord of Improvements or
alterations permanently installed and incorporated in the realty of the
Expansion Premises or the Premises, including space plans and working drawings
of the Expansion Premises (excluding specifically fixtures, furniture and
equipment), as contemplated under the plans and specifications and working
drawings to be prepared by an architect selected by Tenant, and subject to
Landlord's reasonable approval, and to be initialed by Tenant and by Landlord
for identification and approval (the "Plans"); provided, however, that Landlord
shall provide Tenant with one space plan for the Expansion Premises at no charge
(the cost of any additional space plans and all working drawings shall be paid
for out of the Construction Credit). Landlord will cause such work (the "Work")
to be performed in a good and workmanlike manner and in accordance with the
Plans, using Landlord's standard building materials (unless otherwise specified
by Tenant), and using one of Landlord's approved contractors for the Building.
All Work performed shall be subject to Landlord's review and approval, including
but not limited to administration of the Work, which administration shall be
subject to a construction management fee payable to Landlord out of the
Construction Credit of one percent (1%) of the Construction Credit, which is
equal to Three Thousand Four Hundred and 50/100 Dollars ($3,400.50). All Work
shall also be subject to the reasonable approval of the architect. If the
Construction Credit is not used within six months of the Commencement Date, the
unused portion shall revert back to Landlord.

        2. In the event the cost of the Work exceeds the Construction Credit,
Landlord agrees to provide an additional Construction Credit (the "Additional
Construction Credit") of up to Three and No/100 Dollars ($3.00) per rentable
square foot, which equals Sixty-eight Thousand Ten and No/100 Dollars
($68,010.00) provided the cost of any such Additional Construction Credit shall
increase the Base Rent under the Lease for the Premises and the Expansion
Premises by amortizing such Additional Construction Credit over the Term at the
rate of eleven percent (11%) per annum, compounded monthly, and further
provided, that Landlord and Tenant shall enter into an amendment to this Lease
memorializing the amount of the Additional Construction Credit used, and the new
Base Rent for the Premises and the Expansion Premises. Any portion of the
Additional Construction Credit used by Tenant shall also be subject to a one
percent (1%) construction management fee payable to Landlord out of the
Additional Construction Credit. Tenant shall have the option of reimbursing
Landlord the Additional Construction Credit amounts provided by Landlord within
thirty (30) days of the final accounting of such costs.

        3. All material and labor selected by Tenant must be readily available
in Denver, Colorado. Tenant agrees that promptly after the execution of the
Modification, Tenant will



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advise Landlord of all selections or designations as to paint, color and
materials, if other than Landlord's standard materials.

        4. Any additional work which Landlord may agree to perform, or cost of
changes or any materials or installations other than Landlord standard materials
or installations which Landlord may agree to obtain over and above the
Construction Credit, or the Additional Construction Credit if utilized by
Tenant, (to be known as "Tenant's Overstandard Work"), shall be procured at a
cost, plus 5% thereof as an administration payment. Costs include but are not
limited to so-called "general conditions" (e.g., trash, clean-up and hauling,
job lighting and power, insurance, safety protection, security and hoists) in
whole or in part apportionable to Tenant's Overstandard Work. If the aggregate
of all Tenant's Overstandard Work to which Landlord agrees is less than
$2,000.00, the whole amount shall be payable promptly after completion of such
work and after Landlord's billing Tenant for the work. If the aggregate of all
Tenant's Overstandard Work exceeds $2,000.00, such aggregate shall be payable
50% upon Tenant's signing with Landlord the agreement under which Landlord
agrees to perform such Tenant's Overstandard Work, and the balance shall be
payable in substantially equal progress payments promptly after Landlord's
billing Tenant for that work. Such payments in either event shall be collectible
as additional obligations which Tenant shall bear pursuant to the Lease, and, if
Tenant defaults in the payment of that work, Landlord shall have (in addition to
all other remedies) the same rights as provided in the Lease in the event of
Tenants' default in the payment of rent. Any Tenant's Overstandard Work shall
also be subject to the terms of the Lease and shall also be subject to
Landlord's approval of plans and specifications as set forth in Paragraph 1
above.

        5. If the Expansion Premises are not ready for occupancy because of
delays attributable to Tenant (such as changes by Tenant to its finish
requirements after approval of the initial design, delays in providing
information or approving space plans and drawings, and like delays, but not
including the architect's reasonable rejection of the Work under Paragraph 1
above) the Expansion Premises Commencement Date shall be the date the Expansion
Premises would have been substantially completed and ready for occupancy in the
absence of such delays, which date is agreed to be May 1, 2000. Failure by
Landlord to complete the tenant finish improvements shall not relieve Tenant of
its duty to pay rent and perform its obligations under the Lease if such failure
is attributable to Tenant's failure to determine its requirements, approve plans
and specifications or otherwise facilitate completion of the tenant finish
improvements. However, if the Expansion Premises are not ready for occupancy
because of delays not attributable to Tenant, Force Majeure, or architect's
reasonable rejection of the Work pursuant to Paragraph 1 above, the Expansion
Premises Commencement Date shall be the first day of the month following the
date the Work is substantially complete and the Expansion Premises are
substantially ready for occupancy. In the event the Expansion Premises
Commencement Date is delayed beyond May 1, 2000, the Termination Date of the
Lease for the Premises and Expansion Premises shall be extended to the date
which is the last day of the month that is seventy-two (72) full months after
the Expansion Premises Commencement Date, and the parties shall enter into an
amendment to the Lease verifying the Expansion Premises Commencement Date and
the Termination Date of the Lease.

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<PAGE>   10

        6. The terms "substantially complete" and "substantial completion" are
defined as the date when construction is sufficiently completed in accordance
with the contract documents, as modified by any change orders agreed to by the
parties, and subject to completion of Tenant's reasonable list of punch-list
items, so that Tenant can occupy the Expansion Premises for the use for which it
was intended.


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