AbstractTo clarify the cause of their impotence, 20 diabetic patients underwent detailed assessments of: diabetic autonomic neuropathy (acetylcholine sweatspot test, pupil test‐PD%, five cardiovascular tests); vascular disease (radioisotope phallogram, response to intracorporeal papaverine); nocturnal penile rigidity; psychiatric disturbance (General Health Questionnaire). Results suggested cause as: vascular 7/20 (35%), vascular and autonomic neuropathy 7/20 (35%), autonomic neuropathy 3/20 (15%), psychiatric disturbance 2/20 (10%), beta‐blockers 1/20 (5%). The sweatspot test appeared to be the most sensitive assessment of autonomic neuropathy. Investigations suggested an alternative aetiology in all cases with a normal sweatspot test. In one patient with autonomic neuropathy, high deep‐artery velocity on Doppler but loss of papaverine‐induced erection, dynamic cavernosography revealed venous leakage; impotence was improved by surgical venous ligation. The results suggest that most impotence in diabetics has an organic basis. The sweatspot test (ideally in conjunction with cardiovascular tests and pupil test) and response to intracorporeal papaverine may identify and categorise most of these patients. Those with normal tests are unlikely to have organic disease and could be referred for psychosexual/psychiatric counselling. Doppler studies may identify those who need investigating for venous leakage. The others could then, in the first instance, be offered one of the recently described non‐invasive devices for overcoming diabetic impotence. Self‐administered intracorporeal papaverine may also be considered, but only a minority of diabetic patients seem