<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

                         Commission File No. 001-12335

                    FOR THE QUARTER ENDED SEPTEMBER 30, 1998

                          BUTLER MANUFACTURING COMPANY

                       Incorporated in State of Delaware

                          BMA Tower - Penn Valley Park
                             Post Office Box 419917
                       Kansas City, Missouri  64141-0917

                             Phone:  (816) 968-3000
               I.R.S. Employer Identification Number:  44-0188420

                     Shares of common stock outstanding at
                         September 30, 1998:  7,460,048


The name, address and fiscal year of the Registrant have not changed since the
last report.


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 12 months, and
(2) has been subject to such filing requirements for the past 90 days.







<PAGE>   2


                                     INDEX
<TABLE>
<CAPTION>


PART I. - FINANCIAL INFORMATION                                                     Page Number

ITEM 1.    Financial Statements

   <S>                                                                               <C>
    (1)    Consolidated Financial Statements (unaudited):


           Consolidated Statements of Operations for the Three and Nine Month
           Periods Ended September 30, 1998 and 1997.                                   3

           Consolidated Balance Sheets as of September 30, 1998 and
           December 31, 1997.                                                           4


           Consolidated Statements of Cash Flows for the Nine Month Periods
           Ended September 30, 1998 and 1997.                                           5

    (2)    Notes to Consolidated Financial Statements                                   6

ITEM 2.    Management's Discussion and Analysis of Financial Condition and
           Results of Operations                                                       7-9

PART II. - OTHER INFORMATION

ITEM 6.    Exhibits and Reports on Form 8-K                                            10

</TABLE>

           In addition to historical information included herein, this report
           contains forward-looking statements and information that are based on
           management's beliefs as well as on assumptions made by and
           information currently available to management.  These forward-looking
           statements and information are within the meaning of the Private
           Securities Litigation Reform Act of 1995.  When used in this report,
           the words "anticipate," "intend," "plan," "believe," "estimate,"
           "project," and similar expressions are intended to identify
           forward-looking statements.  Such statements are not guarantees of
           future performance and involve certain risks, uncertainties and
           assumptions which could cause the company's future results and
           stockholder values to differ materially from those expressed in such
           forward-looking statements.

           For additional comments, refer to the October 15, 1998 letter to
           shareholders, which is attached as exhibit 19.







                                     Page 2






<PAGE>   3


                 BUTLER MANUFACTURING COMPANY AND SUBSIDIARIES

                     CONSOLIDATED STATEMENTS OF OPERATIONS

     For the three and nine month periods ended September 30, 1998 and 1997

                                  (unaudited)
                   ($000's omitted except for per share data)


<TABLE>
<CAPTION>
                                                           Three months ended           Nine months ended
                                                              September 30,                September 30,

                                                       -----------------------      ----------------------
                                                          1998          1997           1998         1997
                                                       ---------     ---------      ---------    ---------
<S>                                                   <C>           <C>            <C>          <C>
Net sales                                              $ 268,054     $ 241,031      $ 700,355    $ 670,211
Cost of sales                                            222,809       197,149        582,121      552,926
                                                       ---------     ---------      ---------    ---------
  Gross profit                                            45,245        43,882        118,234      117,285


Selling, general and administrative expenses              32,007        30,513         91,611       88,166
                                                       ---------     ---------      ---------    ---------
  Operating income                                        13,238        13,369         26,623       29,119


Other income (expense), net                                (245)            68            406          297
Gain on sale of Grain Systems                                ---           ---            ---       22,000
                                                       ---------     ---------      ---------    ---------
  Earnings before interest and taxes                      12,993        13,437         27,029       51,416
Interest expense                                           1,420           950          4,288        3,860
                                                       ---------     ---------      ---------    ---------
  Pretax earnings                                         11,573        12,487         22,741       47,556
  

Income tax expense                                         4,840         5,681          9,931       19,862
                                                       ---------     ---------      ---------    ---------
  Net earnings                                         $   6,733     $   6,806      $  12,810    $  27,694
                                                       =========     =========      =========    =========

Basic earnings per common share                        $     .89     $     .87      $    1.68    $    3.61
                                                       =========     =========      =========    =========
Diluted earnings per common share                      $     .88     $     .86      $    1.67    $    3.57
                                                       =========     =========      =========    =========

 Basic weighted average number of shares               7,564,700     7,786,297      7,627,038    7,662,786
 Diluted weighted average number of shares             7,618,435     7,871,803      7,691,510    7,753,125
</TABLE>


Net earnings from operations, which excludes the gain on the sale of the Grain
Systems division, was $14,395 or $1.85 per share, for the nine months ended
September 30, 1997.


          See Accompanying Notes to Consolidated Financial Statements.








                                     Page 3







<PAGE>   4


                 BUTLER MANUFACTURING COMPANY AND SUBSIDIARIES
                          CONSOLIDATED BALANCE SHEETS

                    September 30, 1998 and December 31, 1997

                                  (unaudited)
                                ($000's omitted)


<TABLE>
<CAPTION>


                                                                        1998            1997
                                                                   ------------    ------------
<S>                                                               <C>            <C>
ASSETS
  Current assets:
    Cash and cash equivalents                                      $     26,762    $      5,515
    Receivables, net                                                    135,096         106,882
    Inventories:
      Raw materials                                                      45,269          38,622
      Work in process                                                     9,547           7,304
      Finished goods                                                     32,134          43,223
      Lifo reserve                                                      (11,893)        (10,858)
                                                                   ------------    ------------
        Total inventory                                                  75,057          78,291
        


    Real estate developments in progress                                 21,653          22,401
    Deferred tax assets                                                   7,811           7,812
    Other current assets                                                 11,785          12,422
                                                                   ------------    ------------
      Total current assets                                              278,164         233,323


Investments and other assets                                             40,900          35,887
Assets held for sale                                                      9,423           9,423
Property, plant and equipment, at cost                                  247,244         239,747
  Less accumulated depreciation                                        (149,872)       (143,408)
                                                                   ------------    ------------
    Net property, plant and equipment                                    97,372          96,339
                                                                   ------------    ------------
                                                                   $    425,859    $    374,972
                                                                   ============    ============


LIABILITIES AND SHAREHOLDERS' EQUITY
  Current liabilities:
    Notes payable                                                  $      1,515    $     21,280
    Current maturities of long-term debt                                  5,861           5,862
    Accounts payable                                                     94,236          72,266
    Dividends payable                                                     1,119           1,069
    Accrued liabilities                                                  65,469          55,846
    Taxes on income                                                       9,179           8,181
                                                                   ------------    ------------
      Total current liabilities                                         177,379         164,504


  Deferred tax liabilities                                                3,561           3,561
  Other noncurrent liabilities                                           15,851          16,423
  Long-term debt, less current maturities                                68,097          33,918


Shareholders' equity:
     Common stock, no par value, authorized 20,000,000
     shares, issued 9,088,200 shares, at stated value                    12,623          12,623
    Cumulative foreign currency translation adjustment                     (372)             26
    Retained earnings                                                   185,517         175,373
                                                                   ------------    ------------
                                                                        197,768         188,022
  Less cost of common stock in treasury, 1,628,152 shares in
   in 1998 and 1,451,205 shares in 1997                                  36,797          31,456
                                                                   ------------    ------------
    Total shareholders' equity                                          160,971         156,566
                                                                   ------------    ------------
                                                                   $    425,859    $    374,972
                                                                   ============    ============
</TABLE>

          See Accompanying Notes to Consolidated Financial Statements.


                                     Page 4






<PAGE>   5

                 BUTLER MANUFACTURING COMPANY AND SUBSIDIARIES
                     CONSOLIDATED STATEMENTS OF CASH FLOWS

          For the nine month periods ended September 30, 1998 and 1997

                                  (unaudited)
                                ($000's omitted)

<TABLE>
<CAPTION>


                                                                                  1998           1997
                                                                              -----------    -----------
<S>                                                                          <C>            <C>
Cash flows from operating activities:
  Net earnings                                                                $    12,810    $    27,694
  Adjustments to reconcile net earnings to net cash used
  in operating activities:
    Depreciation and amortization                                                  11,012          9,127
    Gain on sale of Grain Systems                                                     ---        (13,299)
    Equity in earnings of joint ventures                                             (156)          (207)
  Change in asset and liabilities, net of businesses acquired and sold:
    Receivables                                                                   (28,214)        (7,606)
    Inventories                                                                     3,234        (18,207)
    Real estate developments in progress                                              748            592
    Other current assets                                                              638         (3,721)
    Current liabilities excluding short-term debt                                  32,591          5,745
                                                                              -----------    -----------  
      Net cash provided by operating activities                                    32,663            118




Cash flows from investing activities:
  Capital expenditures                                                            (10,301)       (20,140)
  Sale of Grain Systems                                                               ---         33,748
  Acquisition of new businesses                                                       ---         (7,697)
  Other, net                                                                       (6,512)        (1,611)
                                                                              -----------    -----------  
      Net cash provided (used) by investing activities                           (16,813)          4,300




Cash flows from financing activities:
  Payment of dividends                                                             (3,214)        (2,751)
  Proceeds from issuance of long-term debt                                         35,000            790
  Repayment of long-term debt                                                        (821)          (533)
  Net change in short-term debt                                                   (19,766)        (4,031)
  Sale and issuance of treasury stock                                                 781            783
  Purchase of treasury stock                                                       (6,121)        (1,035)
  Other, net                                                                          (64)         2,618
                                                                              -----------    -----------  
      Net cash provided (used) by financing activities                              5,795        (4,159)


  Effect of exchange rate changes on cash                                           (398)          (860)
                                                                              -----------    -----------  
    Net increase (decrease) in cash and cash equivalents                           21,247          (601)
  Cash and cash equivalents at beginning of year                                    5,515          2,013
                                                                              -----------    -----------  


Cash and cash equivalents at September 30                                     $    26,762    $     1,412
                                                                              ===========    ===========
</TABLE>

SUPPLEMENTAL SCHEDULE OF NONCASH INVESTING AND FINANCING ACTIVITIES:
The company purchased all of the capital stock of Modu-Line Windows, Inc. on
June 11, 1997  for 191,777 shares of the company's common stock issued from the
treasury, plus deferred cash payments and closing costs totaling $.5 million.
The company also retired Modu-Line's existing bank debt of $4.5 million. In
conjunction with the acquisition, the value of treasury stock issued is shown
below:

    Fair value of assets acquired                                     $11,982
    Cash paid                                                           4,982
                                                                      -------
    Treasury stock issued for purchase of capital stock               $ 7,000
                                                                      =======



          See Accompanying Notes to Consolidated Financial Statements.

                                     Page 5






<PAGE>   6


                 BUTLER MANUFACTURING COMPANY AND SUBSIDIARIES
                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

NOTE 1 - BASIS OF PRESENTATION
The accompanying unaudited consolidated condensed financial statements have been
prepared in accordance with the accounting policies described in the
consolidated financial statements and related notes included in Butler
Manufacturing Company's 1997 Form 10-K.  It is suggested that those consolidated
statements be read in conjunction with this report.  The year-end financial
statements presented were derived from the company's audited financial
statements.  In the opinion of management, the accompanying consolidated
financial statements reflect all adjustments necessary for a fair presentation
of the financial position of Butler Manufacturing Company and the results of its
operations.

NOTE 2 - NEW ACCOUNTING PRONOUNCEMENT
Derivative Instruments and Hedging Activities 
In June, 1998 the Financial Accounting Standards Board issued Statement No. 133,
"Accounting for Derivative Instruments and Hedging Activities." This new
statement replaces existing pronouncements and practices with an integrated
accounting and reporting standard for derivatives and hedging activities.   It
requires that every derivative instrument be recorded in the balance sheet as
either an asset or liability at its fair value, and changes in a derivative's
fair value be recognized in current earnings or other comprehensive income. The
company is required to adopt Statement No. 133 starting January 1, 2000.    The
company does not expect adoption of this standard to have a material impact on
the company's financial statements.

Comprehensive Income
In June, 1997 the Financial Accounting Standards Board issued FASB Statement No.
130, "Reporting of Comprehensive Income" which requires reporting and display of
comprehensive income and its components in a full set of financial statements.
The company has adopted this statement as of January 1, 1998 as required.
"Foreign Currency Translation Adjustment" is the company's only comprehensive
income item as defined by the statement.  Comprehensive income, including after
tax adjustments for foreign currency translation losses, was $6.8 million and
$6.7 million, for the quarters ending September 30, 1998 and 1997, respectively,
and $12.6 million and $27.1 million for the nine month periods ending September
30, 1998  and September 30, 1997, respectively.

NOTE 3 - ACQUISITION AND DISPOSITION OF BUSINESS
On June 11, 1997 the company announced the acquisition of Modu-Line Windows,
Inc. for 191,777 shares of Butler stock having a market value of approximately
$7 million, plus deferred cash payments and closing costs totaling $.5 million.
The company also retired Modu-Line's existing bank debt of approximately $4.5
million.  The fair value of assets acquired of $12 million consisted primarily
of receivables, inventory, and equipment valued at $6.2 million with the
remaining amount allocated to goodwill which will be amortized over 40 years.

On June 23, 1997 the company sold the business and substantially all of the
assets and liabilities used in the business of the Grain Systems division, an
unincorporated division of the company, to CTB, Inc., a privately owned company
in Indiana.  The business was sold for approximately $34 million in cash.  The
sale of the Grain Systems division generated an after-tax gain of $13.3 million,
or $1.72 per share.  Net cash proceeds to the company were approximately $23
million.



                                     Page 6





<PAGE>   7

ITEM 2.  MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND
                             RESULTS OF OPERATIONS

LIQUIDITY AND CAPITAL RESOURCES
Cash and cash equivalents increased $21.2 million in the first nine months of
1998, primarily due to the $35 million private placement of senior notes secured
at the end of the first quarter and used to pay down the company's short-term
line of credit and fund working capital requirements. For the nine months ended
September 30, 1998 domestic short term borrowings averaged $20 million for 118
days compared to $23 million for 242 days in 1997.

In June, 1998 the company amended its existing bank credit agreement to extend
its expiration date to June, 2001 and to reduce the credit available to $40
million from $50 million. As of September 30, 1998 $1.8 million of the domestic
credit line was utilized to provide a bank letter of credit to secure insurance
obligations. The company also maintains a separate line of credit of
approximately $2.5 million for its United Kingdom subsidiary. Management
believes the company's operating cash flow, along with bank credit lines, is
sufficient to meet future liquidity requirements.

Capital expenditures were $10.3 million for the first nine months of 1998
compared to $20.1 million a year ago.  Total capital expenditures are projected
to be approximately $16 million in 1998 compared to actual expenditures of $30
million in 1997. Capital expenditures were greater a year ago due to costs
incurred to increase capacity in the domestic and international metal buildings
businesses, as well as the Architectural Products segment.

Through early October, 1998 the company had repurchased 312,000 shares of its
common stock and had 299,000 shares remaining under the current repurchase
authorization.

On September 15, 1998 the Board of Directors voted to increase the company's
regular quarterly dividend to $.15 per share of common stock payable on October
15, 1998  to shareholders of record as of the close of business on  October 1,
1998.

The Board also declared a dividend distribution of one preferred share purchase
right for each outstanding share of common stock, to replace its rights plan
which expired on September 30, 1998. The dividend was made to holders of record
of common  shares on October 1, 1998 upon expiration of  the outstanding rights.
The rights will be exercisable only if a person or group acquires 15% or more of
Butler's common stock or announces a tender offer, the consummation of which
will result in ownership by a person or group of 15% or more of the common
stock.  The rights will expire on September 30, 2008.

RESULTS OF OPERATIONS
Net sales of $268 million for the quarter ended September 30, 1998 increased 11%
compared to the same quarter a year ago.  The Building Systems, Architectural
Products, and Construction Services segments all contributed to the increase in
sales.  For the nine months ended September 30, 1998 net sales were $700
million, an increase of 8% from last year excluding prior year sales of Grain
Systems which was sold in June, 1997.

The third quarter 1998 consolidated gross profit of $45.2 million compared to
$43.8  million recorded a year ago.  For the nine months ended June 30, 1998
consolidated gross profit was $118.2 million compared to $117.3 million in 1997.
The increase in gross profit in the Building Systems, Construction Services and
Architectural Products segments, offset the loss of gross profits from the Grain
Systems division sale.





                                     Page 7






<PAGE>   8


The Building Systems segment's earnings increased on modestly higher sales due 
to a 10.7% increase in the domestic metal buildings division's earnings during 
the first nine months of the year. Improved results from the domestic metal 
buildings business, Lester wood framed buildings division, and export 
operations offset losses in the company's Brazilian building systems business.  
The Construction Services segment reported higher earnings for the nine month 
period due in part to more effective project execution. Earnings were also 
higher for the continuing operations in the Architectural Products group.

Net earnings from operations for the quarter ended September 30, 1998 were $6.7
million or $.88 per common share, which were comparable with the same period a
year ago.  Net earnings from operations for the nine months ended September 30,
1998  were $12.8 million or $1.67 per common share compared to net operating
income of $14.4 million or $1.85 per common share last year, excluding $13.3
million or $1.72 per common share from the gain on the sale of the Grain Systems
division.  Third quarter and year-to-date 1998 net earnings from operations were
lower due to a delay in closing the sale of sizable Butler Real Estate projects
anticipated to be accomplished in September.  One of these projects closed in
October.

Total backlog of $327 million on September 30, 1998 was up 3% from a year ago.
Product backlog was 5% higher which balanced the construction backlog which was
10% lower.

YEAR 2000 UPDATE 
Many computer systems used by companies, governments and individuals around the
world use only the last two digits to refer to a year ("98" for 1998).
Therefore, these computer programs may not properly distinguish between a year
that begins with "20" versus one beginning with "19".  If not corrected, many
computer applications could fail or create erroneous results. This has come to
be known as the "Year 2000 (Y2K) problem."

The company believes it has identified, or has processes in place to identify,
and will be able to address all of its critical Information Technology, Other
Technology, and Business Issues Year 2000 problems in a timely manner.  Costs
incurred and expected to be incurred in remediation of the company's Year 2000
problems are expected to be immaterial.

In 1997 the company reviewed its principal business, manufacturing, and
engineering computer systems and applications to determine the impact of the
Year 2000 problem on these systems, and to establish a plan to address critical
issues ("Compliance Plan").  In early 1998, the company engaged a consultant to
assess the company's Compliance Plan and its progress toward effecting the Plan
in a timely manner.   The consultant looked at three areas:  Information
Technology ("IT"), such as the company's business, telecommunications,
manufacturing and engineering systems; Other Technology ("Non-IT") such as
manufacturing equipment which contained embedded micro-controllers; and Business
Issues related to service providers, vendors and customers. The consultant
advised the company that nothing was identified that in and of itself would
indicate that the company would not be successful with its Year 2000 compliance
efforts.

In mid-1998 the company established a Year 2000 Project Office responsible for
the day-to-day oversight and coordination of the Y2K Compliance Plan, including
assessment, remediation or compliance (which includes testing), and reporting
efforts.  This office reports to the Executive Vice President of the Company and
the Company's Board of Directors.   A manager at each company business unit has
been assigned the responsibility for coordination and reporting on  "IT",
"Non-IT", and "Business Issue" compliance efforts, including any contingency
plans if needed.  Status reports are reviewed, evaluated and summarized monthly
by the Y2K Project Office.

     INFORMATION TECHNOLOGY:  The assessment phase of the IT process was
     completed in 1997. The company is currently in the remediation or
     compliance phase.  Currently, individual business units are at various
     stages of compliance.  However, it is estimated that in total the company
     is approximately 40% complete with the compliance phase of the project.



                                     Page 8








<PAGE>   9


     OTHER TECHNOLOGY:  The assessment phase of the Non-IT process began in
     1998.  This started with an inventory of all computer controlled and
     networked manufacturing equipment to determine if date functions existed in
     their controllers and whether they were compliant.  This phase of the
     Non-IT process is  substantially complete.  Subsequent phases include
     remediation of equipment controls which are non-compliant.  To-date  it is
     estimated that in total the company is approximately 60% complete with all
     phases of the Non-IT plan, including remediation.

     BUSINESS ISSUES:  The assessment of the Business Issues portion of the Y2K
     plan began in 1998. This phase of the company's plan began with
     identification of key service providers, vendors, and customers by each
     business unit. Company business units have begun to contact key service
     providers, vendors, and customers to assess their Y2K readiness.  To-date
     the company is approximately 10% complete with all phases of its Business
     Issues plan.

Successful completion of the company's Y2K Compliance Plan is dependent upon
timely Year 2000 compliance by key third parties.  If  they are not compliant
there could be a material adverse effect on the company's business, results of
operations, or financial condition.  The Compliance Plan also requires the
company to consider its potential liability to third parties if it is not Year
2000 compliant.  These determinations and assessments are still underway as
noted above.  Finally, the Compliance Plan requires the company to identify its
most reasonably likely worst case Year 2000 problem scenarios and to develop a
contingency plan to handle them.  These scenarios have yet to be identified or
contingency plans, if needed, created.

MANAGEMENT TRANSITION
In September, 1998 the Board of Directors elected Paul F. Liljegren Treasurer of
the company.  Mr. Liljegren,  previously Vice President - Controller of the
company's Lester Building Systems Division, replaces Larry C. Miller who was
elected Vice President - Finance in June, 1998.





                                     Page 9








<PAGE>   10


PART II. - OTHER INFORMATION

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

     (a)   Exhibits

           (19) October 15, 1998 letter to shareholders

           (27) Financial Data Schedule

     (b) Reports on Form 8-K

         The company filed a report on Form 8-K on September 23, 1998 disclosing
         the declaration of a dividend of one preferred share purchase right for
         each outstanding share of common stock.






                                    Page 10







<PAGE>   11


                                   SIGNATURES

Pursuant to the requirement 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.



BUTLER MANUFACTURING COMPANY



November 12, 1998                            /s/ Larry C. Miller
-----------------                            -----------------------------------
Date                                         Larry C. Miller
                                             Vice President - Finance
                                             and Chief Financial Officer



November 12, 1998                            /s/ Richard O. Ballentine
-----------------                            -----------------------------------
Date                                         Richard O. Ballentine
                                             Vice President, General Counsel
                                             and Secretary





                                    Page 11







<PAGE>   12

                                                                      Exhibit 99

                                 EXHIBIT INDEX


Exhibit
Number              Description
-------             ---------------------------------------

19                  October 15, 1998 Letter to Shareholders

27                  Financial Data Schedule