This study aimed to examine the psychometric values of a Farsi-translated version of the International Index of Erectile Function among a population sample of Iranian men. A community sample of 2,345 healthy men and a clinical sample of 421 men with diagnosed erectile function from 2 cities of Iran participated in the study. Participants were asked to complete the International Index of Erectile Function, the Life Satisfaction questionnaire, and a demographic questionnaire at baseline. Four weeks later, both samples were asked to recomplete the International Index of Erectile Function. The response rates were 84% (n = 1,969) and 98% (n = 412) for healthy men and men with erectile function, respectively. The retest reliability of the International Index of Erectile Function showed excellent intraclass correlation coefficients for both the healthy and patient samples. The International Index of Erectile Function subscales correlated significantly with the scores resulting from the clinical rating of erectile function conducted by urologists. Men with erectile function, as diagnosed by urologists, had significant lower scores in all subscales. The results of the exploratory factor analysis indicated that the International Index of Erectile Function could be summarized into a 5-component solution.The Iranian version of the International Index of Erectile Function was found to be a highly valid and reliable instrument to be used for the assessment of erectile function in clinical and population samples.