The association between smoking and erectile dysfunction was evaluated in a cohort of 2,115 Caucasian men, aged 40-79 years, randomly selected from Olmsted County, Minnesota. Smoking status was assessed by questionnaire; during the fourth biennial examination, erectile dysfunction was assessed with the Brief Male Sexual Function Inventory. Of the 1,329 men with a regular sexual partner, 173 were current smokers, 836 had previously smoked, and 203 reported erectile dysfunction. Compared with former and never smokers, current smokers in their forties had the greatest relative odds of erectile dysfunction, 2.74 (95% confidence interval (CI): 0.44, 16.89), compared with 1.38 (95% CI: 0.51, 3.74), 1.70 (95% CI: 0.82, 3.51), and 0.77 (95% CI: 0.27, 2.21) for men in their fifties, sixties, and seventies, respectively. Compared with men who never smoked, men who smoked at some time had a greater likelihood of erectile dysfunction (age-adjusted odds ratio = 1.42, 95% CI: 1.00, 2.02), and there was a dose response. Although the causal pathway underlying this association is not clear, this study contributes to the growing literature describing an association between smoking and erectile dysfunction.