Objectives. To assess the validity of severity classes on the erectile function (EF) domain of the International Index of Erectile Function by determining their relationship with the self-assessment of EF, before and after treatment, in an independent cohort of patients.

Methods. Two hundred forty-seven men with clinically diagnosed erectile dysfunction (ED) and in a stable heterosexual relationship were enrolled in a randomized, double-blind, multicenter, placebo-controlled, parallel-group, 12-week, flexible-dose study. Patients assessed their degree of ED as severe, moderate, minimal/mild, or no problem at baseline and after treatment. They also responded to the six questions of the EF domain, with the total score indicating the following degrees of ED: severe, EF score 1 to 10; moderate, EF score 11 to 16; mild to moderate, EF score 17 to 21; mild, EF score 22 to 25; and no ED, EF score 26 to 30. Descriptive profiles of the two diagnostic instruments were compared. The correlations between the instruments were evaluated with Kendall’s tau-b at baseline, after treatment at 12 weeks, and at change from baseline.

Results. The two measures gave generally similar descriptive profiles of ED severity. The correlations were 0.65 (95% confidence interval 0.57 to 0.73) at baseline, 0.86 (95% confidence interval 0.83 to 0.89) after 12 weeks of treatment, and 0.73 (95% confidence interval 0.67 to 0.79) at change from baseline.

Conclusions. The moderate-to-high correlation between the patients’ self-assessment of EF and the EF domain of the International Index of Erectile Function provides a validation of this domain for the reliable diagnostic classification of ED severity.