OBJECTIVE: This study sought to determine whether differential treatment effects in the targeted mechanisms of change and eating disorder (ED) symptoms are associated with patterns of attrition from a RCT. METHOD: The main study was a RCT of a psychotherapy designed to alter the non-weight related self-cognitions as the means to promote recovery and health in a sample of 69 women with AN or BN. Four groups based on point of dropout were compared on demographic, self-cognitions and ED symptoms using logit and piecewise mixed effects modeling. RESULTS: Attrition was highest during treatment phase but no significant predictors were found. During the measurement phase, the direction and amount of change in self-cognition interrelatedness and body dissatisfaction differed according to point of dropout and treatment group. DISCUSSION: Attention to changes both in symptoms and mediating factors that occur during treatment and follow-up may help to identify those who are at risk for dropout and to develop strategies to promote RCT participant retention.