In the US, men who have sex with men (MSM) comprise the largest proportion of new HIV infections, with black MSM being infected at significantly higher rates. Differences in sexual-risk behaviors and substance use do not explain the disproportionate HIV rates by race among MSM. The most likely explanations are low frequency of HIV testing, high HIV prevalence within sexual networks, high prevalence of other sexual transmitted infections (STIs), and barriers to health care access and HIV/STI treatment. These result in later diagnoses of HIV-infected men, more frequent STIs, and fewer HIV-infected men having access to care.