Given the high rate of co-occurring major depression in patients with panic disorder, it is unclear whether patterns of comorbidity in individuals with panic disorder reported in the literature are associated with panic disorder or with the presence of major depression. Subjects were 231 adult subjects with panic disorder and major depression (n=102), panic disorder without comorbid major depression (n=29), major depression without comorbid panic disorder (n=39), and neither panic disorder nor major depression (n=61). Subjects were comprehensively assessed with structured diagnostic interviews that examined psychopathology across the life cycle. Panic disorder, independently of comorbidity with major depression, was significantly associated with comorbid separation anxiety disorder, simple phobia, obsessive-compulsive disorder, generalized anxiety disorder, and agoraphobia. Major depression, independently of comorbidity with panic disorder, was significantly associated with comorbidity with psychoactive substance use disorders and childhood disruptive behavior disorders. Overanxious disorder was associated with both panic disorder and major depression. Major depression has important moderating effects on patterns of comorbidity of panic disorder in referred adults.