Correspondence is a relation between one representation and another (McCarthy & Prince 1993, 1994, 1995). This relationship may be between an underlying or lexical representation and a surface representation, that is: Input–Output forms; or between surface forms such as a reduplicant and its base (McCarthy & Prince 1995) or other derivationally related pairs (see for example Benua 1995, McCarthy 1995, Kenstowicz 1996) – i.e. Output–Output. Correspondence constraints over related words in a paradigm ensure uniformity within the paradigm. In earlier theories this effect was ensured by the Strict Cycle Constraint, which forbade structure-changing operations except in immediately derived environments and thus ensured that most of the base word stayed the same in derivation. In this paper we show that correspondence between derivationally related output forms (Benua 1995) is essential for the proper analysis of vowel length in Warray, a language of Northern Australia spoken near Darwin, and superior to an account making use of cyclicity. Correspondence constraints ensuring identity between output forms explain the pattern of vowel length in nouns, predicting both where long vowels occur as well as the apparently anomalous appearance of short vowels where long vowels might be expected.