Sexual function was studied in 175 diabetic male outpatients randomly selected. Data collected included medical and sexual histories, physical examination, complete blood count, urinalysis, T4, 12 channel chemistry screening profile and plasma testosterone determination. Eighty-five of the 175 men were impotent (49 per cent), four reported premature ejaculation (2 per cent) and two subjects had retrograde ejaculation (1 per cent). In the group with impotence, the mean age of the subjects and duration of diabetes were respectively fifty-three and six years. In patients without impotence, the comparable values were fortyfive and five years. Typically, the onset of impotence was gradual, usually progressing over a period of six months to a year with an interval during which firmness of erection was decreased. Levels of sexual interest were sustained in almost all subjects. Over 90 per cent of the males studied gave a pattern of impotence compatible with an organic rather than a psychologic etiology. Occurrence of impotence'was not definitely correlated with duration of diabetes or with insulin or oral agents. Incidence of peripheral neuropathy was increased in the group with sexual dysfunction. Plasma testosterone levels were within normal limits in impotent diabetics or in the group without impotence, respectively (mean ± S.E.M.) 627 ±15 and 637 ± 14 ng per cent. It is apparent from these findings that androgen deficiency was not an etiologic factor in this group of diabetic men with impotence.