This study compares the heterosexual risk behaviors, perceptions of vulnerability to HIV/AIDS, and predictors of condom use of two groups of women with very different sexual and contraceptive histories and habits–college women and women in Marine Corps recruit training. The Marines' s]exual behaviors put them at greater risk of contracting HIV than the college students; that is, Marines reported more frequent intercourse with more partners, used condoms less frequently, and had less knowledge about HIV/AIDS transmission. Consistent with these differences, college students displayed a larger illusion of unique invulnerability than did the Marines. In general, the women who had more sexual partners and more frequent sexual intercourse were less likely to report regularly using condoms. In addition, the data provide support for Weinstein and Nicholich's (1993) recent suggestion that the relation between risk perception and risk behavior is different for different groups of people.