Sailors are a mobile population travelling a lot and therefore being often exposed to casual sex. The aim of this study is to analyze the determinants of unprotected sex among sailors in Senegal. A descriptive and analytical study was conducted among sailors of the merchant navy. Data on knowledge, attitudes and practices were collected during a personal interview. A multivariate analysis was performed using a multiple logistic regression. A total of 400 sailors were interviewed, 57.9% had casual sex of whom 23.7% were not protected. Sexual intercourse without protection was more common among the uneducated (OR = 2.29 [1.23 to 5.99]) and married (OR = 2.29 [1.23-5.99]). Sailors who thought that using condom reduces pleasure during sexual intercourse (OR = 2.5 [1.2-5.1]) and those who consumed alcohol (OR = 5.4 [2.07-14.2]) were less protected during casual sex. Sexual contact is one of the main modes of transmission of HIV / AIDS. Sailors often have unprotected sex. Interventions using specific ways must be performed taking into account the mobility of these men who are often uneducated.