The relationship between therapeutic alliance, therapist adherence to treatment protocol, and outcome was analyzed in a randomized trial of cognitive-behavioral therapy (CBT) and interpersonal psychotherapy for bulimia nervosa. Independent observers rated audiotapes of full-length therapy sessions. Purging frequency was the primary outcome variable. There were no significant therapist or Therapist x Treatment effects on outcome. Although results showed high levels of alliance and adherence across treatments, CBT was associated with greater adherence. Across treatments and time points, better adherence was associated with enhanced alliance. Treatment condition and baseline purging frequency, but not adherence, predicted outcome. Early alliance predicted posttreatment purging frequency. In temporal analyses, prior symptom change assessed early in treatment was significantly related to subsequent adherence at midtreatment.