Panic disorder was diagnosed in 26 of 200 Ss with a chief complaint of chronic fatigue, a frequency 10 times greater than that in the general population. Compared with the rest of the study group, more Ss with panic disorder had a history of severe depression including persistent thoughts of death or suicide. Findings suggest that treatable panic disorder is an important contributor not only to major depression & somatization, but also to the etiology & clinical presentation of chronic fatigue.