The purpose of this research was to determine the prevalence of erectile dysfunction (ED) in a non-selected population using the abridged 5-item version of the International Index of Erectile Function (IIEF-5) as a diagnostic tool. In a non-institutionalized population and during a free screening program for prostate cancer (Prostate Cancer Awareness Week of Santa Casa Hospital, Porto Alegre, Brazil), from 26 to 30 July 1998, all men who were attending were invited to complete a sexual activity questionnaire (the abridged 5-item version of the International Index of Erectile Function-IIEF-5) as a diagnostic tool for ED. The possible scores for the IIEF-5 range from 5 to 25, and ED was classified into five categories based on the scores: severe (5-7), moderate (8-11), mild to moderate (12-16), mild (17-21), and no ED (22-25). Of the 1071 men who participated in the program, 965 (90.1%) were included in this study. Of the responding men 850 were Caucasian (88%) and 115 were black (12%). The mean age of the men was 60.7 y, ranging from 40 to 90 y old. In this sample the prevalence of all degrees of ED was estimated as 53.9%. In this group of men, the degree of ED was mild in 21.5%, mild to moderate in 14.1%, moderate in 6.3%, and severe in 11.9%. According to age the rates of ED were: 40-49 (36.4%); 50-59 (42.5%); 60-69 (58.1%); 70-79 (79.4%), and over 80 y (100%) showed ED (P<0.05). The Pearson coefficients between the variables age and IIEF-5 showed a statistically significant inverse (negative) relation (r=-0.3449; P<0.05). ED is highly prevalent in men over 40 and this condition showed a clear relationship to aging, as demonstrated in other studies published. The simplified IIEF-5, as a diagnostic tool, showed to be an easy method, which can be used to evaluate this condition in studies with a great number of men.