The relationship between depression and disability in idiopathic Parkinson's disease (PD) was examined in 31 outpatients. Thirteen percent had current major depression (MD), 10% dysthymia, and 32% a lifetime history of MD. Depression was significantly related to both illness severity and functional impairment. Male patients with early-onset PD (before age 55) had more mood and anxiety disorders than late-onset male patients. Patients with right-sided PD had significantly move depressive symptoms than those with left-sided PD. On multiple regression analyses, depression predicted impaired social, role, and physical functioning for men (but not for women), independent of the impact of illness severity. The results suggest that treatment of depression may improve function; however, findings of gender differences will require replication.