Background: Seafarers constitute a highly mobile population who are vulnerable to acquiring and transmitting human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) due to their engagement in HIV risk behaviors. Hence, this study aimed to identify the determinants of HIV risk behaviors among seafarers. Materials and Methods: The study was conducted among Nigerian seafarers in Port Harcourt Seaport, Rivers State Nigeria. A qualitative study was employed using a total of four focus group discussions (FGDs) and comprised of three male groups and one female group. Snow-ball method of sampling was used to recruit participants. Data were collected using a FGD guide. Thematic analysis was performed using QSR NVivo version 10 software (QSR International Pty Ltd., Melbourne, Australia). Data were presented as quotes and charts. Results: The study had a total of 28 participants and comprised of 24 males and four females. The mean age of all participants was 39.3 ± 7.8 years. The participants were knowledgeable on HIV/AIDS risk behaviors. The major determinants of these behaviors as revealed by the participants were lack of self-discipline and not being God-fearing (individual-level factors). Other determinants were long duration (more than 6 months) on sea and not traveling with spouse during sea voyage (seafaring-related factors). The determinants on environment of the port and government-related factors included the presence of brothels in port areas and the absence of sensitization visits, respectively. Conclusion: The study noted varying determinants of HIV risk behaviors from individual level to the government level. The authors advocate the need for peer education among seafarers as well as the implementation of HIV enlightenment programs to discourage HIV risk behaviors.