Rapid response to treatment, indicated by substantial decreases in eating-disorder (ED) symptoms within the first 4-6 weeks of treatment, is the most reliable predictor of treatment outcomes for EDs. However, there is limited research evaluating short-term longitudinal trajectories of ED symptoms during treatment. Thus, it is difficult to know which aspects of ED psychopathology are slow or fast to change. The purpose of this study was to elucidate three-month trajectories of ED psychopathology during treatment and test whether ED diagnosis influenced the direction and rate of change.