To estimate the incidence of erectile dysfunction (ED) in Brazilian men 40 to 69 years old at study entry during an average 2-year follow-up and study the effect of age, socioeconomic status, and medical conditions on the risk of developing ED. METHODS: We analyzed data from a randomly sampled cohort of men living in Salvador, Bahia (Brazil), a racially diverse city with a population of 2.3 million. A total of 602 men completed the baseline interview in 1998 and 501 completed follow-up in 2000. The analysis sample consisted of 428 (83.4%) of 513 men without ED at baseline. The men were interviewed in person, using a standardized questionnaire, and ED was assessed by a single global self-rating question. RESULTS: The crude incidence rate for ED was 65.6 cases per 1000 person-years (95% confidence interval 49.6 to 85.2). The incidence rate increased with age and was 33.3, 53.7, and 189.5 cases per 1000 person-years for men 40 to 49, 50 to 59, and 60 to 69 years old, respectively. The age-adjusted risk of developing new-onset ED was higher for men with lower education, diabetes, hypertension, and benign prostatic hyperplasia. Population projections for men 40 to 69 years old suggest that approximately 68,600 new cases of ED in Bahia and 1,025,600 in Brazil would be expected annually. CONCLUSIONS: The incidence of ED in Brazilian men was 2.5-fold higher than that in the Massachusetts Male Aging Study (26/1000 person-years) and increased with age, lower education, diabetes, hypertension, and benign prostatic hyperplasia.