<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM THE BALANCE
SHEET, STATEMENT OF OPERATION AND STATEMENT OF CASH FLOWS INCLUDED IN CIENA'S
FORM 10-Q FOR THE PERIOD ENDING JULY 31, 1999, AND IS QUALIFIED IN ITS ENTIRETY
BY REFERENCE TO SUCH FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000

                             
<PERIOD-TYPE>                   3-MOS
<FISCAL-YEAR-END>                          OCT-31-1999
<PERIOD-START>                             MAY-01-1999
<PERIOD-END>                               JUL-31-1999
<CASH>                                         142,599
<SECURITIES>                                   155,657
<RECEIVABLES>                                  104,684
<ALLOWANCES>                                     1,528
<INVENTORY>                                     64,638
<CURRENT-ASSETS>                               497,178
<PP&E>                                         204,224
<DEPRECIATION>                                  75,891
<TOTAL-ASSETS>                                 644,897
<CURRENT-LIABILITIES>                           88,775
<BONDS>                                              0
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                         1,373
<OTHER-SE>                                     541,021
<TOTAL-LIABILITY-AND-EQUITY>                   644,897
<SALES>                                        128,826
<TOTAL-REVENUES>                               128,826
<CGS>                                           79,361
<TOTAL-COSTS>                                   79,361
<OTHER-EXPENSES>                                61,442
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                                 200
<INCOME-PRETAX>                                (8,485)
<INCOME-TAX>                                   (2,928)
<INCOME-CONTINUING>                            (5,557)
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                   (5,557)
<EPS-BASIC>                                     (0.04)
<EPS-DILUTED>                                   (0.04)