This paper analyzes the perceptions of risk for HIV transmission and the formation of sexual identities and gender of young men and women of different sexual orientations and color/race. The study is based on ethnographic observation in a variety of nocturnal social environments in Rio de Janeiro and interviews with young people within this context. The findings show that our informants have assimilated preventive information regarding HIV, but have difficulties in adopting consistent condom use. There are variations in HIV risk perception associated with sexual identities and gender: gay men see themselves and are perceived by others as the most vulnerable group. Among youth who claim heterosexual practices, susceptibility to HIV is associated with “others”. Lesbians see themselves as not being at risk for AIDS. It can be concluded that sexual identities and gender influence the perception of AIDS risk. However, being social, sexual identities are contextual and can vary over the course of a person’s life. Our results underscore the importance of the current debate regarding the implications of fixing identity labels to social and political movements.