The present study was performed to compare the clinical features of patients with panic disorder with and without agoraphobia. The subjects were 233 outpatients with panic disorder (99 males and 134 females) diagnosed according to DSM-IV criteria. Sixty-three patients met the criteria for panic disorder without agoraphobia, and 170 met the criteria for panic disorder with agoraphobia. Patients with agoraphobia showed a significantly longer duration of panic disorder and higher prevalence of generalized anxiety disorder. However, there were no significant differences in prevalence of major depressive episodes, in current severity of panic attacks, or in gender ratio between the two groups. The second aim of the present study was to investigate the effects of onset age and sex differences on the development of agoraphobia within a half-year. The subjects were divided into two groups according to their self-report: patients who did or did not develop agoraphobia within 24 weeks of onset of panic disorder. A total of 40.6% of the patients developed agoraphobia within 24 weeks of the onset of panic disorder, and onset age and sex differences had no robust effect on the development of agoraphobia within 24 weeks.