Diabetic impotence is generally presumed to be secondary to peripheral abnormalities of the vascular or autonomic nervous system, although central nervous control of the autonomic nervous system has not previously been studied. Measures of rapid eye movement (REM) sleep as potential indicators of central autonomic dysfunction were studied along with sleep-related tumescence for 10 impotent diabetics, nine psychogenically impotent men, and 10 men whose impotence was secondary to pelvic trauma. Low REM density was found in the diabetics with REM density correlating with measures of tumescence. These results suggest that central autonomic dysfunction may be a contributing factor in the impotence of diabetic men. A metabolic disturbance in the central nervous system of diabetics which might alter both sleep and autonomic nervous system activity is proposed to explain these results and may help in the understanding of other observed abnormalities in both the sleep and autonomic dysfunction of diabetics.