OBJECTIVES: With increasing international travel it is important to understand how frequent casual travel sex and unprotected intercourse are, and what impact this may have on the risk of acquiring sexually transmitted infections (STIs). METHODS: We conducted a systematic review, and where appropriate meta-analyses, to ascertain the influence of foreign travel on behavior, including new partnerships, unprotected intercourse, and STI acquisition. RESULTS: The pooled prevalence of travel-associated casual sex was 20.4% (95% confidence interval (CI) 14.8-26.7%), with 49.4% (95% CI 38.4-60.5%) of these having unprotected intercourse. The predominant characteristics of people who had new sexual partners abroad were: young age, male gender, single status, and traveling alone or with friends, with a previous history of multiple sexual partners or an STI. People who travel or stay abroad for longer periods and men who have sex with men are at higher risk of developing new sexual partnerships and having unprotected intercourse. The risk of developing an STI is increased up to 3-fold in people who experience casual travel sex. CONCLUSIONS: New sexual partnerships and unprotected intercourse abroad are relatively common. People who develop new sexual partnerships and have unprotected intercourse abroad have an increase risk of STIs. There is, however, a paucity of information related to strategies to prevent the risk of STI acquisition during foreign travel.