Many men who have sex with men (MSM) are among those who increasingly use the internet to find sexual partners. Few studies have compared behavior by race/ethnicity in internet-based samples of MSM. We examined the association of race/ethnicity with HIV risk-related behavior among 10,979 Hispanic, black, and white MSM recruited online. Significant variations by race/ethnicity were found in: age, income level, sexual orientation, number of lifetime male and female sexual partners, and rates of unprotected anal intercourse (UAI). Black and Hispanic men were more likely to report anal intercourse during the last sexual encounter, but white men were more likely to report UAI. In multivariate analysis, UAI was associated with HIV infection and sex with a main partner. Significant risk behavior variations by race/ethnicity were found. Research is needed to better target online interventions to MSM who engage in UAI or have other risk factors for transmitting or acquiring HIV.