This paper presents a theory of morphophonology based on a development in the theory of faithfulness in Optimality Theory. A new constraint type, anti-faithfulness, is proposed that evaluates a pair of related words and requires an alternation in the shared stem. This constraint type is motivated initially by a set of problems, e.g. morphological deletions, segmental exchanges and non-structure preserving processes, which show that morphophonology must encompass more than markedness–faithfulness interactions. The anti-faithfulness thesis is then applied to accentual processes in which affixes idiosyncratically cause deletion of accent in a neighbouring morpheme. It is argued that anti-faithfulness both motivates the observed deletion and accounts for its properties with principles that are generally available in phonological theory. Anti-faithfulness is then shown to extend naturally to the analysis of other affix-induced alternations, including accent insertions, shifts, and retractions of stress and tone, a result which distinguishes this theory from plausible alternatives.