HIV infection is associated with sexual dysfunction. Using validated instruments, we investigated the relationship between HIV/AIDS and sexual function in a contemporary cohort of men who have sex with men (MSM). An anonymous Internet-based survey was disseminated to MSM via organizations and social networking sites that cater to this population. Information on ethnodemographic variables, health status (including HIV status, disease stage, and other health conditions), and sexual behavior was collected. Men were categorized as HIV-negative, HIV-positive/AIDS-negative, or HIV-positive /AIDS-positive. A modified validated version of the International Index of Erectile Function (IIEF) for use in MSM and the Premature Ejaculation Diagnostic Tool (PEDT) were used to stratify risk of sexual dysfunction. The study cohort included 1361 men (236 of whom were HIV-positive) who provided complete data on HIV status, IIEF, and PEDT. There was a significant trend toward greater prevalence of erectile dysfunction (ED) in men with progressive HIV infection 40-59 years of age relative to age matched HIV-negative men (p=0.02). In a logistic regression model controlling for other variables, HIV infection without AIDS was not associated with greater odds of ED; however, HIV infection with AIDS was associated with greater odds of ED (p=0.006). In a separate logistic regression model, HIV infection with or without AIDS was not significantly associated with greater odds of premature ejaculation (p>0.05). Use of phosphodiesterase 5 (PDE5) inhibitor drugs was much more common in HIV-infected men. HIV infection is a risk factor for poorer sexual function primarily due to higher risk of erectile dysfunction in men with AIDS.