Prevalence of impotence was assessed among 292 consecutive diabetic men attending the Tikur Anbessa Hospital, diabetic clinic. The mean age was 41.4 +/- 15.5 years (range 18-86 years). One hundred and forty nine (51.6%) were type I and 143 (49%) were type II patients. The mean duration of diabetes was 9.9 +/- 6.7 years and 37.7% had known long term diabetic complications. The overall prevalence of impotence was 48.7%. The mean duration of impotence was 3.5 +/- 3.4 years. In the majority of the cases, impotence started after diagnosis of diabetes mellitus. Many of the patients (79.1%) had never complained to physicians and 59.2% of the patients did not know that impotence is a complication of diabetes mellitus. All except 10 patients (7.5%) had libido. Impotence is significantly higher in type II as compared to type I patients (94/143 versus 40/132, p < 0.001) and in patients with complications than without (76/104 versus 54/159, p < 0.001). The mean duration of diabetes mellitus is significantly higher in patients with impotence than without impotence (12.3 years versus 8.1 years, p < 0.001). We conclude that impotence is a common and significant problem in our diabetic men and we recommend further study to assess its social and psychiatric impact.