We examined the relationship between cigarette smoking and erectile physiology in 314 men with erectile dysfunction. All of the men studied were currently cigarette smokers. Evaluations included interviews, physical examinations, and polysomnographic assessment of sleep-related erections. Penile rigidity during nocturnal erection inversely correlated with the number of cigarettes smoked per day. Smoking was also associated with indices of impairment on autonomic function tests and some measures of penile blood pressure. The group of men who smoked the most (more than 40 cigarettes per day) had the fewest minutes of nocturnal tumescence and detumesced fastest. These data are discussed with respect to the results of studies performed in dogs that demonstrated smoking-related reduction in arterial flow and venous restriction. Our findings suggest that smoking may further compromise penile physiology in men experiencing difficulty in maintaining erections long enough for satisfactory intercourse.