OBJECTIVE To evaluate the prevalence, clinical correlates, and severity of sexual dysfunction in combat veterans with and without post-traumatic stress disorder (PTSD) using a validated instrument for assessing sexual function. The results of recent studies have suggested that combat veterans with PTSD experience a higher rate of sexual dysfunction than do those without PTSD. METHODS We administered the International Index of Erectile Function (IIEF) and a demographic and health questionnaire to male combat veterans undergoing treatment for PTSD and to age-comparable male combat veterans without PTSD. RESULTS The mean total IIEF score was significantly lower in the 44 patients with PTSD than in the 46 controls (26.38 versus 40.86; P = 0.035). With respect to the individual IIEF domains, patients with PTSD had poorer scores on overall satisfaction and orgasmic function and showed trends toward poorer scores on intercourse satisfaction and erectile function. No statistically significant difference was observed for sexual desire. The rate of erectile dysfunction was 85% in patients with PTSD and 22% in controls. Moderate to severe erectile dysfunction was present in 45% of the patients with PTSD and in only 13% of controls. Significantly more patients with PTSD (57%) than controls (17%) were using psychotropic medications. CONCLUSIONS Combat veterans with PTSD experience a significantly higher rate of sexual dysfunction than do veterans without PTSD and show impairment in some, but not all, specific domains of sexual function. The IIEF may be useful in evaluating the response to treatment of erectile dysfunction. Clinicians should proactively address the sexual concerns of combat veterans with PTSD.