We evaluated 31 male diabetics for sexual dysfunction. Patients were examined by an endocrinologist, psychologist or psychiatrist, urologist and neurophysiologist. Evaluation was done by penile blood pressure, pudendal nerve latency, psychologic testing and laboratory tests, including serum testosterone levels. Mean patient age was 53 years and the average onset of sexual dysfunction was 6 years after the diagnosis of diabetes. Results showed that 68 per cent of the patients had evidence of vascular occlusion, 26 per cent had neurologic abnormalities, 19 per cent had low plasma testosterone levels and 38 per cent had relevant psychological problems, although the condition was considered primarily psychogenic in only 19 per cent. Of those patients with abnormal nerve latencies 86 per cent had abnormal Doppler penile systolic pressures, while only 28 per cent of the patients with abnormal penile pressures had abnormal neurologic findings. These data suggest that vascular occlusion is the most prevalent abnormality in impotent diabetics and may predate neurologic abnormalities. The diabetics were divided into 2 groups, insulin-dependent and insulin-nondependent patients. A higher incidence of vascular lesions was found in insulin-dependent diabetics (83 versus 57 per cent), suggesting that vascular pathological conditions are related to severity of the diabetes. Although most diabetics have a vascular etiology for impotence one must remember that other causes may be present and that a thorough investigation is necessary.