The stigma associated with male sex workers (MSW) hinders the prevention, treatment, and care of HIV infection in this population. These factors make social and public health resources less accessible to MSW. To improve the effectiveness of prevention strategies, this study examines social factors such as educational level, country of origin, and sexual orientation. Semi-structured interviews of 100 MSW in Castellón and Valencia (Spanish cities) indicate that knowledge of HIV transmission is good; nevertheless, MSW significantly overestimate or underestimate some sexual practices. Levels of condom use are high; notably, they are higher during anal sex. Levels of condom use are lower with intimate partners than with clients. MSW do not present differences in terms of the socio-demographic variables analyzed and sexual orientation. Furthermore, regression analyses are not significant. These results offer more accurate profiles of MSW than were previously available, which will ultimately help improve the effectiveness of prevention programs.