Panic disorder comorbid with other psychiatric conditions appears to be more common than panic disorder alone. Depression is the most frequently associated disorder. This article reviews the detrimental effects of comorbidity on the severity and course of panic disorder. The presence of comorbidity results in more severe anxiety and depressive symptoms, a higher rate of suicide attempts, a higher frequency of other comorbid conditions, and a poorer response and compliance to treatment. Thus, it is important for physicians to be aware of the possibility of comorbidity in patients with panic disorder in order to select the most appropriate therapy to target all components of their condition.