Given the significant high risks of both being exposed to the virus and spreading it, mariners traveling across countries on a regular basis fall into one of the top-priority populations of those to whom education on HIV/AIDS should be given. However, there have been no reports regarding HIV/AIDS knowledge and attitudes on the part of mariners in Turkey. Therefore, this study was carried out with the aim of defining the knowledge and attitudes of 660 Turkish mariners. Data were determined using a self-completed questionnaire. Percentage and mean scores were used in data analysis. Results show that the mariners' knowledge was inadequate (mean score was 52.31 +/- 20.46 over a total of 100 points). The lowest knowledge pertained to HIV/AIDS prevention (mean score was 44.62 +/- 19.97). About half of the mariners considered themselves to be in the risk group. Very few of them (10%) have had an AIDS test. Most (68%) were informed about HIV/AIDS by the media. These results show that the mariners need to increase HIV/AIDS knowledge about prevention, transmission, treatment information, motivation, and behavioral skills to decrease HIV/AIDS risky behaviors. The mariners had the least knowledge about HIV/AIDS protection. Having a critical role in preventing the transmission and spreading of diseases, nurses should conduct more extensive and advanced research into HIV/AIDS and assume educational and counseling responsibilities in illuminating society.