It was suggested that fatigue is one of characteristics of panic disorder. Fatigue was assessed in 360 patients with panic disorder using the Japanese version of the Multidimensional Fatigue Inventory (MFI-J). The scores for general fatigue and reduced activity were significantly higher in the patients than in the controls. These tendencies were also observed in men when the subject group was differentiated according to sex, but not in women. In contrast, the trend for higher score for physical fatigue was observed only in the female patients. Thus, the present study suggests that the characteristics of fatigue vary with sex in panic disorder.