We conducted a prospective cohort study to assess sexual behaviour of students at a British University during the summer break, to explore the role of foreign travel as a risk factor of sexually transmitted infections acquisition and to determine characteristics associated with casual sex. We found that those who travelled abroad were more likely to use alcohol (RR 1.59, 95% CI 1.17–2.16) and cannabis (RR 1.35, 95% CI 1.13–1.62) and to have casual sex during holidays. They also reported more sexual relationships after holidays (RR 1.26, 95% CI 1.09–1.53). New partnerships during holidays were associated with being single, foreign travel, drinking alcohol and having previously had large number of sexual partners. The adjusted relative risk of developing new sexual partnerships with foreign travel was 2.70 (95% CI 1.11–6.61). People who travel abroad during holidays are more likely to engage in risk taking behaviour and have casual sex. They are also more sexually active after holidays.