International travelers engaging in casual sex are at risk for acquiring sexually transmitted diseases (STDs), including HIV. The frequency of international travel emphasizes the need for a travel sexual activity history to be included in the clinical assessment of any returned traveler. When formulating a differential diagnosis, the STD prevalence rates at the travel destination and the risk profile of the traveler and the sexual partner need to be considered. Casual sex with host country nationals residing in tropical and subtropical areas of the developing world increases the traveler's risk for acquiring STDs rarely seen in industrialized countries, particularly bacterial genital ulcer diseases. Pretravel counseling needs to include education on STD prevention. A post-travel STD diagnostic evaluation is indicated when casual sexual activity has occurred during travel, regardless of whether symptoms are present.