High-risk sexual activity, including engaging in transactional sex, concurrent sexual partnerships, and inconsistent condom use, increases the risk of infection with HIV and other sexually transmitted infections (STI). The demands of seafaring, such as long periods spent away from home, and the availability of commercial sex around seaports, can contribute to a culture of high-risk activity such as multiple casual sexual encounters and poor condom use. In 2005 and 2008, the Kiribati Ministry of Health conducted HIV and STI prevalence and behaviour surveys among seafarers. The results suggest that, while knowledge of HIV prevention and transmission improved from 2005 to 2008, this did not correlate with reduced levels of risky sexual activity in the same period. These findings suggest that HIV and STI prevention programs must extend beyond providing information, and testing and treatment facilities, towards implementing strategies that encourage and support safer sexual behaviours amongst seafarers and their partners, in particular transactional sex partners.