Comorbid conditions require attention in the planning of treatment strategies for panic disorder, as they affect the course and prognosis of the disorder as well as its response to treatment. The literature documents high rates of comorbidity for depression, bipolar disorders, generalized anxiety disorder, social phobia, other anxiety disorders, and personality disorders (especially dependent and avoidant personality disorders). The alcohol abuse research shows comorbidity rates that are lower than expected from clinical reports. Although agoraphobia is no longer considered a comorbid disorder, its presence with panic disorder represents more severe disturbance and involves a higher likelihood of one or more comorbid diagnoses. The disorders of depression and panic are usually more severe when they co-occur than when only one is present. Research on the role of specific comorbid conditions in the outcome of treatment for panic disorder is reviewed.