The present study investigated the sexual risk behaviors of men who have sex with men (MSM) traveling to a popular gay tourist destination in the United States. In 2004, a brief survey was administered to 247 MSM tourists recruited from gay-oriented venues in Key West, Florida. Data collected included demographics, HIV status, length of stay, substance use, and sexual risk behaviors. A probabilistic model of HIV transmission was used to translate participants' reports of their sexual behaviors while in Key West into estimates of their risk of acquiring HIV. Twenty-two percent of participants reported anal sex with multiple partners over a relatively brief period (M = 4.1 days), and approximately one third reported having sex with a partner met during the vacation period. Modeling analyses suggested that sexual activity among vacationing MSM would account for approximately 201 new HIV infections among MSM visitors to Key West each year. Although previous studies have documented sexual risk behavior in travelers, quantitative estimates of the impact of these behaviors on the spread of HIV are lacking. Findings suggest that the risk-taking behavior of MSM on vacation may play an important role in the dissemination of HIV and other sexually transmitted diseases (STDs). Future research should assess additional factors (e.g., use of highly active antiretroviral therapy) that may affect HIV transmission in MSM travelers. In addition, efforts are needed to develop effective risk-reduction interventions for this population.