<TABLE> <S> <C>

<PAGE>
<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY INFORMATION EXRACTED FROM THE CONSOLIDATED
STATEMENTS OF OPERATIONS AND CONSOLIDATED BALANCE SHEETS OF MEDIACOM LLC AND
SUSIDIARIES AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL
STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
       
<S>                             <C>                     <C>                     <C>
<PERIOD-TYPE>                   12-MOS                   12-MOS                   9-MOS
<FISCAL-YEAR-END>                          DEC-31-1997             DEC-31-1996             DEC-31-1998
<PERIOD-START>                             JAN-01-1997             MAR-12-1996             JAN-01-1998
<PERIOD-END>                               DEC-31-1997             DEC-31-1996             SEP-30-1998
<CASH>                                            1027                     396                     968
<SECURITIES>                                         0                       0                       0
<RECEIVABLES>                                      674                     292                    2474
<ALLOWANCES>                                        56                      25                     467
<INVENTORY>                                       1032                       0                       0
<CURRENT-ASSETS>                                     0                       0                       0
<PP&E>                                           51735                   18993                  216900
<DEPRECIATION>                                  (5737)                   (1056)                 (26136)
<TOTAL-ASSETS>                                 102791                     46560                 447666      
<CURRENT-LIABILITIES>                                0                       0                       0
<BONDS>                                              0                       0                       0
<PREFERRED-MANDATORY>                                0                       0                       0
<PREFERRED>                                          0                       0                       0
<COMMON>                                             0                       0                       0
<OTHER-SE>                                       24441                    4537                   91539
<TOTAL-LIABILITY-AND-EQUITY>                    102791                   46560                  447666
<SALES>                                          17634                    5411                   94374
<TOTAL-REVENUES>                                 17634                    5411                   94374
<CGS>                                             5547                    1511                   32873
<TOTAL-COSTS>                                    16761                    4869                   99652
<OTHER-EXPENSES>                                   640                     967                    3838     
<LOSS-PROVISION>                                     0                       0                       0
<INTEREST-EXPENSE>                                4829                    1528                   17786
<INCOME-PRETAX>                                 (4586)                  (1953)                 (26902)
<INCOME-TAX>                                         0                       0                       0
<INCOME-CONTINUING>                             (4596)                  (1953)                 (26902)
<DISCONTINUED>                                       0                       0                       0
<EXTRAORDINARY>                                      0                       0                       0
<CHANGES>                                            0                       0                       0
<NET-INCOME>                                    (4596)                  (1953)                 (26902)
<EPS-PRIMARY>                                        0                       0                       0
<EPS-DILUTED>                                        0                       0                       0
        

</TABLE>