The authors' goal was to identify predictors of treatment response in bulimia nervosa and, in particular, to attempt to replicate and extend the observation that early change predicts outcome. Predictors of response at the end of treatment and 8-month follow-up were sought from a group of 220 women treated with either cognitive behavior therapy or interpersonal psychotherapy. Early change in frequency of purging was the best predictor of response at the end of treatment and at 8-month follow-up. Early change in treatment is a robust and potent predictor of immediate and longer-term outcome in bulimia nervosa.