A concise, reliable means of assessing erectile dysfunction (ED) in large, multidisciplinary population-based studies is needed. A single, direct question for self-assessed ED was assessed in the population-based sample of the Massachusetts Male Aging Study (MMAS). Of the 1156 respondents to the 1995-97 MMAS follow-up evaluation, 505 were randomly selected to complete either the International Index of Erectile Function (IIEF) (n = 254), or the Brief Male Sexual Function Inventory (BMSFI) (n = 251), in addition to the single question self-assessment. The proportion not classified due to missing data was MMAS-9%, BMSFI-8%, and IIEF-18%. The single question correlated well with these other measures (r = 0.71-0.78, P < 0.001). Prevalence was similar to that based on the IIEF, agreement was moderate (kappa = 0.56-0.58), and associations with previously identified risk factors were similar for each classification. Thus, the MMAS single question may be a practical tool for population-based studies where detailed clinical measures of ED are impractical.