<PAGE>   1

                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

                                    FORM 10-Q

                  QUARTERLY REPORT UNDER SECTION 13 OR 15(d) OF
                       THE SECURITIES EXCHANGE ACT OF 1934


For quarter ended June 30,1998                  Commission File Number 0-13147
                  ------------                                         --------

                                   LESCO, INC.
--------------------------------------------------------------------------------
             (Exact name of registrant as specified in its charter)

            OHIO                                        34-0904517
------------------------------          ---------------------------------------
State or other jurisdiction of          (I.R.S. Employer Identification Number)
incorporation or organization)

           20005 Lake Road
           Rocky River, Ohio                               44116
----------------------------------------                 ----------
(Address of principal executive offices)                 (Zip Code)

                                 (440) 333-9250
                         -------------------------------
                         (Registrant's telephone number,
                              including area code)


Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding twelve months (or for such shorter period that the registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days. Yes  X  No
                                       ---    ---


Indicate the number of shares outstanding of each of the issuer's classes of
common stock, as of the close of the latest practical date.

                                                       Outstanding at
                Class                                 August 13, 1998
   --------------------------------                   ----------------
   Common shares, without par value                   8,356,116 shares





                                       1
<PAGE>   2



                                   LESCO, INC.
                           CONSOLIDATED BALANCE SHEETS

<TABLE>
<CAPTION>
                                                                        June 30          June 30         December 31
(In thousands except share data)                                         1998             1997              1997
                                                                     -----------      ------------      ------------
                                                                             (unaudited)
<S>                                                                   <C>               <C>               <C>      
ASSETS

CURRENT ASSETS:
     Cash                                                             $   3,102         $   4,600         $   3,403
     Accounts receivable -- net                                          82,873            72,696            65,869
     Inventories                                                         98,813            86,649            82,174
     Deferred income taxes                                                2,742             4,734             2,680
     Prepaid expenses and other assets                                    1,846             1,422             5,989
                                                                      ---------         ---------         ---------
         TOTAL CURRENT ASSETS                                           189,376           170,101           160,115

Property, Plant and Equipment                                            68,140            50,321            58,454
     Less allowance for depreciation and amortization                   (29,320)          (26,482)          (27,238)
                                                                      ---------         ---------         ---------
                                                                         38,820            23,839            31,216
     Bond proceeds held for construction                                    341                 -             4,761
                                                                      ---------         ---------         ---------
                                                                         39,161            23,839            35,977

Other Assets                                                              8,703             4,979             4,226
                                                                      ---------         ---------         ---------

         TOTAL ASSETS                                                 $ 237,240         $ 198,919         $ 200,318
                                                                      =========         =========         =========

LIABILITIES AND SHAREHOLDERS' EQUITY

CURRENT LIABILITIES:
     Accounts payable                                                 $  66,021         $  55,952         $  34,002
     Other current liabilities                                            7,716            10,684             8,202
     Current portion of  debt                                               200               200               200
                                                                      ---------         ---------         ---------
         TOTAL CURRENT LIABILITIES                                       73,937            66,836            42,404

Long-term debt                                                           82,895            63,429            83,353
Deferred income taxes                                                     2,282             1,627             2,268

SHAREHOLDERS' EQUITY:
     Preferred shares-- without par value--
         authorized 500,000 shares
     Common shares--without par value--
         19,500,000 shares authorized; 8,395,560 shares issued
         and 8,389,832 outstanding at June 30, 1998, 8,151,847
         at June 30, 1997, 8,250,356 at December 31, 1997                   839               815               825
     Paid-in capital                                                     31,143            27,576            29,268
     Retained earnings                                                   47,075            38,987            42,347
     Less treasury shares                                                   (59)              (17)              (59)
     Unearned compensation                                                 (872)             (334)              (88)
                                                                      ---------         ---------         ---------

         TOTAL SHAREHOLDERS' EQUITY                                      78,126            67,027            72,293
                                                                      ---------         ---------         ---------

         TOTAL LIABILITIES AND
         SHAREHOLDERS' EQUITY                                         $ 237,240         $ 198,919         $ 200,318
                                                                      =========         =========         =========
</TABLE>



                                       2
<PAGE>   3



                                   LESCO, INC.
                              STATEMENTS OF INCOME

<TABLE>
<CAPTION>
                                             Three Months Ended June 30        Six Months Ended June 30
                                              -------------------------       -------------------------

     (In Thousands, Except per Share Data)      1998            1997            1998            1997
                                              ---------       ---------       ---------       ---------
                                                   (unaudited)                        (unaudited)

<S>                                           <C>             <C>             <C>             <C>      
Net sales                                     $ 134,446       $ 111,128       $ 207,136       $ 176,395
                                            
Cost of sales                                    88,709          74,332         136,883         117,347
                                              ---------       ---------       ---------       ---------
                                            
     GROSS PROFIT ON SALES                       45,737          36,796          70,253          59,048
                                            
Selling, general and                        
     administrative expenses                     32,891          25,893          58,805          49,096
                                              ---------       ---------       ---------       ---------
                                            
     INCOME FROM OPERATIONS                      12,846          10,903          11,448           9,952
                                            
Other deductions (income):                  
     Interest expense                             1,319           1,075           3,044           2,324
     Other - net                                   (497)           (459)         (1,124)         (1,005)
                                              ---------       ---------       ---------       ---------
                                                    822             616           1,920           1,319
                                              ---------       ---------       ---------       ---------
                                            
Income Before Income Taxes                       12,024          10,287           9,528           8,633
                                            
Income taxes                                      4,690           4,012           3,716           3,367
                                              ---------       ---------       ---------       ---------
                                            
                                            
     NET INCOME                               $   7,334       $   6,275       $   5,812       $   5,266
                                              =========       =========       =========       =========
                                            
                                            
                                            
     BASIC EARNINGS PER SHARE                 $    0.88       $    0.77       $    0.70       $    0.65
                                              =========       =========       =========       =========
                                            
     DILUTED EARNINGS PER SHARE               $    0.85       $    0.74       $    0.67       $    0.63
                                              =========       =========       =========       =========
</TABLE>



                                       3
<PAGE>   4


                                   LESCO, INC.
                      CONSOLIDATED STATEMENTS OF CASH FLOWS


<TABLE>
<CAPTION>
                                                                   Six Months Ended
                                                                       June 30
                                                              --------------------------
(In Thousands)                                                  1998            1997
                                                              ---------       ---------
                                                                    (unaudited)
<S>                                                           <C>             <C>      
OPERATING ACTIVITIES:
     Net income                                               $   5,812       $   5,266
     Adjustments to reconcile net income to net cash
         used by operating activities:
         Depreciation and amortization                            2,667           2,044
         Increase in accounts receivable                        (17,809)        (16,529)
         Provision for uncollectible accounts receivable          1,055           1,257
         Increase in inventories                                (15,445)        (18,559)
         Increase in accounts payable                            31,799          29,166
         Increase in other current items                          3,615           4,005
         Other                                                      464            (146)
                                                              ---------       ---------

     NET CASH PROVIDED IN OPERATING ACTIVITIES                   12,158           6,504

INVESTING ACTIVITIES:
     Purchase of property, plant and equipment - net             (8,268)         (2,591)
     Acquisition of businesses                                   (8,174)              -
     Bond proceeds held for construction                          4,420               -
                                                              ---------       ---------

     NET CASH USED BY INVESTING ACTIVITIES                      (12,022)         (2,591)

FINANCING ACTIVITIES:
     Proceeds from borrowings                                   131,897          40,000
     Reduction of borrowings                                   (132,355)        (41,275)
     Issuance of common shares                                    1,105           1,035
     Cash Dividend                                               (1,084)           (973)
                                                              ---------       ---------

     NET CASH USED BY FINANCING ACTIVITIES                         (437)         (1,213)
                                                              ---------       ---------

Net (Decrease) Increase in Cash                                    (301)          2,700

Cash --  Beginning of the Period                                  3,403           1,900
                                                              ---------       ---------

     CASH - END OF THE PERIOD                                 $   3,102       $   4,600
                                                              =========       =========
</TABLE>



                                       4
<PAGE>   5


                                   LESCO, INC.
                          NOTES TO FINANCIAL STATEMENTS
                          -----------------------------


NOTE A - Basis of Presentation
------------------------------

The accompanying unaudited financial statements have been prepared in accordance
with generally accepted accounting principles for interim financial information
and with the requirements of Regulation S-X and Form 10-Q. The statements
reflect all adjustments, consisting only of normal recurring accruals, which
are, in the opinion of management, necessary for a fair presentation of the
results for interim periods. For further information, refer to the audited
financial statements and footnotes thereto for the year ended December 31, 1997
included in the Company's Form 10-K.

Operating results for the six months ended June 30 are not necessarily
indicative of the results to be expected for the year due to the seasonal nature
of the Company's business.

NOTE B - Earnings per Share
---------------------------

The following table sets forth the computation of basic and diluted earnings per
share:

<TABLE>
<CAPTION>
                                                           Three Months Ended June 30             Six Months Ended June 30
         (In thousands except share data)                      1998             1997               1998                1997
         ------------------------------------------ ------------------- ------------------ ------------------- -------------------

<S>                                                          <C>                <C>                 <C>                 <C>      
         Numerator:
            Net Income                                          $7,344             $6,275              $5,812              $5,266
         Denominator:
            Denominator for basic
              earnings per share -
              weighted average shares                        8,326,488          8,101,555           8,292,741           8,081,209

            Effect of dilutive securities:
              Employee stock options                           330,674            326,966             356,293             288,395
              Performance shares                                18,301             18,301              18,301              18,301
                                                    ------------------- ------------------ ------------------- -------------------
            Diluted potential common
              shares                                           348,975            345,267             374,594             306,696
            Denominator for diluted
              earnings per share -
              adjusted weighted average
              shares and assumed
              conversions                                    8,675,463          8,446,822           8,667,335           8,387,905
         Earnings per share
            Basic                                                $0.88              $0.77               $0.70               $0.65
            Diluted                                              $0.85              $0.74               $0.67               $0.63
</TABLE>


                                       5
<PAGE>   6


NOTE C - Acquisitions
---------------------

On January 30,1998, the Company acquired certain assets of Agriturf, Inc. and
Cadwell & Jones, Inc. for $6.0 million in cash, plus the assumption of $2.2
million of debt. The asset purchase included land, a fertilizer manufacturing
facility and related warehouse, working capital and manufacturing equipment. The
asset purchase was financed by the Company's credit facility.







                                       6
<PAGE>   7





                                   LESCO, INC.
                  FINANCIAL CONDITION AND RESULTS OF OPERATIONS
                      MANAGEMENT'S DISCUSSION AND ANALYSIS
                      ------------------------------------


Results of Operations
---------------------

THREE MONTHS ENDED JUNE 30, 1998 COMPARED WITH
THE THREE MONTHS ENDED JUNE 30, 1997

Net sales for the three-month period ended June 30, 1998 of $134.4 million
increased 21.0% over the net sales of $111.1 million for the same period in
1997. The increase in net sales is due to volume increases which reflect strong
demand for fertilizer and control products, with other products growing at a
slower pace. The Company had 235 Service Centers in operation for the
three-month period ended June 30, 1998 compared to 215 Service Centers in
operation for the same period a year ago. Comparable store sales increased 12.4%
for the three-month period ended June 30, 1998.

Gross profit for the second quarter of $45.7 million, constituting 34.0% of
sales, increased 24.2% over the $36.8 million gross profit, constituting 33.1%
of sales, for the same period in 1997. The gross profit percentage increase
occurred primarily in control products due to cost reductions associated with a
higher volume of purchases.

Selling, general and administrative expenses of $32.9 million increased 27.0%
over the $25.9 million incurred during the same period in 1997. Expense
increases are largely attributable to expenses associated with the addition of
20 new Service Centers and two additional Stores-on-Wheels(R) for 1998, and
increases in the Company's distribution and freight expenses associated with
higher level of sales. During the first six months, the Company relocated its
distribution center in New Jersey and moved its distribution center in Sebring,
Florida in order to consolidate Florida operations closer to its manufacturing
site. Both of these events also contributed to the higher level of expense.

Interest expense was $1.3 million in the current quarter compared with $1.1
million a year ago and is largely attributable to increased debt levels
associated with the August 1, 1997 acquisition of the Tri Delta operation in
California, and the January 30, 1998 Agrifturf and Cadwell & Jones asset
purchases, the construction of the Company's new plant facility in Sebring,
Florida, and increases in working capital associated with sales increases
compared to a year ago. Other deductions - net consist primarily of customer
finance charges which totaled $723,000 for the three month period ended June 30,
1998 and $625,000 in 1997.

The effective tax rate for both the second quarter of 1998 and 1997 was 39.0%

Primarily as a result of the factors above, the Company's net income for the
three-month period ending June 30, 1998 of $7.3 million represents an increase
of 16.9% compared to the $6.3 million earned a year earlier.



                                       7
<PAGE>   8


SIX MONTHS ENDED JUNE 30, 1998 COMPARED WITH
THE SIX MONTHS ENDED JUNE 30, 1997

Net sales for the six-month period ended June 30, 1998 of $207.1 million
increased 17.4% over the net sales of $176.4 million for the same period in
1997. The increase in net sales is due to volume increases which reflect strong
demand for fertilizer and control products, with other products growing at a
slower pace. The Company had 235 Service Centers in operation for the six-month
period ended June 30, 1998 compared to 215 Service Centers in operation for the
same period a year ago. Comparable store sales increased 10.6% for the six-month
period ended June 30, 1998.

Gross profit for the six-month period ended June 30, 1998 of $70.3 million,
constituting 33.9% of sales, increased 19.2% over the $59.0 million gross
profit, constituting 33.5% of sales, for the same period in 1997. The gross
profit percentage increase occurred primarily in control products due to cost
reductions associated with a higher volume of purchases.

Selling, general and administrative expenses of $58.8 million increased 19.8%
over the $49.1 million incurred during the same period in 1997. Expense
increases are largely attributable to expenses associated with the addition of
20 new Service Centers and two additional Stores-on-Wheels(R) for 1998, and
increases in the Company's distribution and freight expenses associated with
higher level of sales. During the first six months, the Company relocated its
distribution center in New Jersey and moved its distribution center in Sebring,
Florida in order to consolidate Florida operations closer to its manufacturing
site. Both of these events also contributed to the higher level of expense.

Interest expense was $3.0 million in the current six-month period compared with
$2.3 million a year ago. The higher interest expense is mainly attributable to
increased bank debt levels associated with the August 1, 1997 acquisition of the
Tri Delta operation in California, and the January 30, 1998 Agriturf and Cadwell
& Jones asset purchases, the construction of the Company's new plant facility in
Sebring, Florida, and increases in working capital associated with sales
increases compared to a year ago. Other deductions - net consist primarily of
customer finance charges which totaled $1.4 million for the six month period
ended June 30, 1998 and $1.2 million in 1997.


The effective tax rate for the current year six-month period was 39.0% compared
with 39.0% for the same period a year ago.

Primarily as a result of the factors above, the Company's net income for the
six-month period ending June 30, 1998 of $5.8 million represents an increase of
10.4% compared to the $5.3 million earned a year earlier.


                                       8
<PAGE>   9




Financial Condition, Liquidity and Capital Resources
----------------------------------------------------

On January 30, 1998, the Company acquired certain assets of Agriturf, Inc. and
Cadwell and Jones, Inc. for $6.0 million in cash, plus the assumption of $2.2
million in debt. The asset purchase included land, a fertilizer manufacturing
facility and related warehouse, working capital, and other manufacturing assets.
Funding for the asset purchase was financed by an extension of the Company's
credit facilities.

As of June 30, 1998, total assets of the Company were $237.2 million compared to
$198.9 million as of June 30, 1997 and $200.3 million as of December 31, 1997.
The asset increase compared to a year ago is primarily attributable to increases
in working capital and increases in property, plant, and equipment associated
with the acquisitions completed by the Company within the past year, while the
increase from December 31, 1997 is primarily due to seasonality. Accounts
receivable were $82.9 million as of June 30, 1998 compared to $72.7 million a
year ago, and $65.9 million as of December 31, 1997. Compared to a year ago,
Accounts receivable have increased by 14.0% compared to the 17.4% increase in
sales. Inventory was $98.8 million as of June 30, 1998 compared to $86.6 million
a year ago, and $82.2 million as of December 31, 1997. Compared to a year ago,
inventory has increased by 20.2% compared to the 17.4% increase in sales. The
increase in inventory reflects the Company's seasonal build combined with
inventory associated with the increase in Service Centers.

Funding for the asset changes was provided primarily by an increase in long-term
debt, along with an increase in accounts payable. The Company's long-term debt
increased to $82.9 million as of June 30, 1998. Accounts payable increased to
$66.0 million as of June 30, 1998 from $56.0 million as of June 30, 1997, and
$34.0 million as of December 31, 1997. The increase in accounts payable
year-over-year was due to inventory purchases related to year-to-year sales
volume while the December to June increase reflects seasonal supplier deferred
payment programs which are due in the second and third quarter of the year.

On June 23, 1998, the Company completed a $50 million private placement of
Senior Notes with five lenders. The Senior Notes have an average life of seven
and one-half years, with average fixed-rate interest of 6.81%. Proceeds of the
Senior Notes were used to reduce the amounts outstanding under the Company's
bank credit facility.

Outstanding debt under the Company's credit facility was $19.1 million as of
June 30, 1998 compared to $57.0 million as of June 30, 1997 and $69.5 million as
of December 31, 1997. As of June 30, 1998, the Company had $60.9 million
available under its bank credit facility. The Company experiences peak seasonal
working capital needs which will reduce in the third quarter and believes its
current borrowing capacity is adequate for the foreseeable future.

Capital expenditures for the first six months of 1998 totaled $8.3 million of
which $2.0 million related to property, plant and equipment purchased in the
Agrifturf, Inc. and Cadwell & Jones, Inc. asset purchases. The primary
expenditure of the remaining $6.3 million included the construction of the new
fertilizer manufacturing facility in Sebring, Florida, improvements in the
Company's information systems and the opening of twenty new Service Centers.


                                       9
<PAGE>   10



Year 2000 Compliance
--------------------

Over the past three years, the Company has broadly implemented new information
systems and technology with respect to production, production planning,
inventory management, order entry, distribution and financial systems. This
broad-based strategic initiative, which also includes noninformation systems,
will be completed by mid 1999. As a result, it is the Company's assessment that
these new systems and technology either have the capability now, or will by the
end of 1998, to adequately recognize the year 2000. The Company does not
currently expect third-party year 2000 compliance issues to have a material
impact on its operation. An internal initiative has been established to continue
to evaluate the potential impact of year 2000 on its operations.

New Accounting Requirements
---------------------------

In June 1997, the Financial Accounting Standards Board issued FAS No. 131,
"Disclosures about Segments of an Enterprise and Related Information." The
statement requires a "management" approach to reporting financial and
descriptive information about a Company's operating segments. Management
continues to study the potential effect of adopting this statement.

As of January 1, 1998 the Company adopted FAS No. 130, "Reporting Comprehensive
Income." The statement establishes new rules for the reporting and display of
comprehensive income and its components. The adoption of this statement had no
impact on the Company's net income or shareholders' equity and the Company has
no elements of other comprehensive income in any period presented.

Forward-Looking Statements
--------------------------

Certain statements included in the report are forward-looking statements that
are based on management's current belief, assumptions and expectations. These
forward-looking statements can be identified by the use of predictive or future
tense terms such as "anticipate," "estimate," "project," "may," "will" or
similar terms. These statements are made pursuant to the safe harbor provisions
of the Private Securities Litigation Reform Act of 1995. The Company's actual
future performance may differ materially from that anticipated in
forward-looking statements. Risk factors that would cause or contribute to such
differences include, but are not limited to:

         -    regional weather conditions which have an impact on both timing
              and volume of sales;

         -    the Company's successful execution of its operating plans;

         -    the Company's ability to integrate business acquisitions
              successfully;

         -    general economic and business conditions;

         -    changes in market demographics; and

         -    changes in the regulation of the Company's products, including
              applicable environmental regulations.


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<PAGE>   11



                           PART II - OTHER INFORMATION
                           ---------------------------

Except as noted below, the items in Part II are inapplicable or, if applicable,
would be answered in the negative. These items have been omitted and no other
reference is made thereto.

Item 4 - Submission of Matters to a Vote of Security Holders
------------------------------------------------------------

On May 13, 1998, the Registrant conducted its Annual Meeting of Shareholders,
The following matters were brought before the shareholders for vote at this
meeting:

         Election of Directors for a One-Year Term
         -----------------------------------------

<TABLE>
<CAPTION>
                                           Votes "For"    Votes "Withheld"
                                           -----------    ----------------
<S>                                        <C>                 <C>    
Ronald Best                                6,436,990           370,470
Drexel Bunch                               6,436,735           370,725
Robert F. Burkhardt                        6,443,859           363,602
Paul H. Carleton                           6,434,348           373,112
David H. Clark                             6,442,451           365,010
J. Martin Erbaugh                          6,377,718           429,742
Michael J. FitzGibbon                      6,443,540           363,920
William A. Foley                           6,443,386           364,074
Lee C. Howley                              6,443,685           363,775
</TABLE>

  Amendment to the 1992 Stock Incentive Plan
  ------------------------------------------
                                  For       Against    Abstain/Broker Non-Votes
                                  ---       -------    ------------------------

1992 Stock Incentive Plan      6,057,239    132,617           132,617

No other matters were brought before shareholders for a vote.

Item 5 - Other Information
--------------------------

         Shareholders who intend to submit proposals included in the Company's
proxy materials may do so in compliance with Rule 14a-8 promulgated under the
Securities Exchange Act of 1934. As stated in the Company's proxy statement
dated April 9, 1998, the last date any such proposal will be received by the
Company for inclusion in the Company's proxy materials relating to the 1999
Annual Meeting is December 8, 1998. For those shareholder proposals which are
not submitted in accordance with Rule 14a-8, the Company's designated proxies
may exercise their discretionary voting authority for any proposal received
after February 23, 1999, without any discussion of the proposal in the Company's
proxy materials.

Item 6 - Exhibits and Reports on Form 8-K
-----------------------------------------

         (a)      Exhibits:
                  (4) (i) $50,000,000 Senior Note Purchase Agreement dated June
                  15, 1998 
                  (10) (r) Sixth Amendment to the Credit Agreement dated June
                  25, 1998
                  (27) Financial Data Schedule




                                       11
<PAGE>   12




                                   SIGNATURES

                  Pursuant to the requirements of the Securities Exchange Act of
1934, the registrant has duly caused this report to be signed on its behalf by
the undersigned thereunto duly authorized.

                                          LESCO, INC.





August 13, 1998                           By:     /s/ Ware H. Grove
----------------                              ----------------------------------
                                          Ware H. Grove, Vice-President/
                                                  Chief Financial Officer




                                       12