Therapist adherence has been shown to contribute to the effectiveness of treatment interventions. The role in a patient’s decision to drop out of treatment, however, is unknown. This study investigates whether therapist adherence affects clinical outcome and the risk for dropout. Patients diagnosed with panic disorder with agoraphobia (N = 265) were treated in one of two CBT variations: with (T+) and without (T-) explicit therapist-guided exposure. Significant associations between lower levels of adherence and symptomatic improvement were observed in treatment completers in the T- condition and dropouts in T+ condition suggesting that adherence-outcome relations are potentially contributed by patient and treatment characteristics. Moreover, our results propose that patient related difficulties with exposure procedures may lead to lower adherence and dropout.