During a fourteen-month period, 497 men were evaluated for a primary complaint of erectile dysfunction. The initial evaluation consisted of a history taken in a conventional manner and supplemented by a patient-completed sexual function questionnaire, a physical examination, and serum testosterone, serum prolactin, and nocturnal penile tumescence studies. When appropriate, additional evaluations, including penile vascular studies, two-hour oral glucose tolerance tests, and psychiatric consultation were obtained. Abnormal glucose metabolism was present in 161 men (32%). Five men (1%) had insulin-dependent diabetes mellitus (IDDM), 80 men (16%) had noninsulin-dependent diabetes mellitus (NIDDM), 55 men (11.1%) had newly diagnosed noninsulin-dependent diabetes mellitus, and 21 men (4.2%) had impaired glucose tolerance tests. One hundred forty-seven of these men (91.3%) had organic pattern impotence, and 14 (8.7%) had psychogenic pattern impotence.