The authors conducted a community-based anonymous survey of 837 men who have sex with men (MSM) to gauge the extent of Viagra (sildenafil citrate) use, its association with high-risk sexual behavior, and its combination with other drugs. Participants' mean age was 35 years, 67% were white, and 66% had a college degree. The majority (76%) reported anal sex in the past 6 months, with 49% reporting always using condoms. Overall, 32% had ever used Viagra (CI: 29%-36%). Significant independent predictors of Viagra use were white race, older age, HIV positivity, illicit drug use, and having had unprotected anal sex with potentially serodiscordant partners. Over one third of Viagra users had combined Viagra with other drugs, 18% with amyl nitrate. Only a minority (44%) obtained Viagra under the care of a physician. For some MSM, Viagra appears to be an emerging contributing factor to unsafe sex, potentially increasing HIV transmission. HIV care and prevention providers should target Viagra users for enhanced education on safer sex and potentially harmful drug interactions.