The International Index of Erectile Function (IIEF) is a widely used, multi-dimensional self-report instrument for the evaluation of male sexual function. It is has been recommended as a primary endpoint for clinical trials of erectile dysfunction (ED) and for diagnostic evaluation of ED severity. The IIEF was developed in conjunction with the clinical trial program for sildenafil, and has since been adopted as the 'gold standard' measure for efficacy assessment in clinical trials of ED. It has been linguistically validated in 32 languages and used as a primary endpoint in more than 50 clinical trials. This review summarizes early stages in the psychometric validation of the instrument, its subsequent adoption in randomized clinical trials with sildenafil and other ED therapies, and its use in classifying ED severity and prevalence. The IIEF meets psychometric criteria for test reliability and validity, has a high degree of sensitivity and specificity, and correlates well with other measures of treatment outcome. It has demonstrated consistent and robust treatment responsiveness in studies in USA, Europe and Asia, as well as in a wide range of etiological subgroups. Although only one direct comparator trial has been performed to date, the IIEF is also sensitive to therapeutic effects with treatment agents other than sildenafil. A severity classification for ED has recently been developed, in addition to a brief screening version of the instrument. This review includes the strengths as well as limitations of the IIEF, along with some potential areas for future research.

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This manuscript covers two complementary topics. For both topics, data from clinical studies and control samples were used. The first topic provides an overview of the development and validation of the International Index of Erectile Function (IIEF), a 15item questionnaire, for male erectile and sexual function. A principal components analysis revealed five factors (erectile function, orgasmic function, sexual desire, intercourse satisfaction, and overall satisfaction). The IIEF demonstrated reliability, validity, and sensitivity and specificity with regard to treatment effect. The second topic presents, among men who reported having had sexual intercourse, the methodology and results on the evaluation of the erectile function (EF) domain of the IIEF; which has a range of scores from 6-30 for these men, as a diagnostic tool to help discriminate between men with and without erectile dysfunction (ED). For a prevalence rate of ED equal to 0.5 in a clinical population, the Classification and Regression Trees program gave a cutoff score of 25: men with EF scores of 25 or less were retrospectively classified as having ED, while those with scores above 25 were classified as not having ED (sensitivity = 0.97, specificity = 0.88). The IIEF has been developed and validated as a scale that is

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