We surveyed 158 college freshmen on an urban campus to determine their sexual practices and their knowledge and attitudes about acquired immunodeficiency syndrome (AIDS). Many students (47%) were heterosexually active; 1% were homosexual, 1% were bisexual, and 51% had not been sexually active. Among the 77 sexually active students, many engaged in activities that can facilitate transmission of human immunodeficiency virus (HIV): 58% did not always use condoms with a new partner; 31% had had two or more sex partners in the last year, 8% engaged in anonymous sex; and 14% of sexually active women had anal intercourse. Although most sexually active students said they would use condoms more or reduce the number of their sexual partners if they believed these changes would reduce 'my risk for getting AIDS' few students had adopted these safer sexual practices. Safer sexual practices were associated with heightened personal concerns about AIDS but not with knowledge, which was at a high level. These findings underscore the need for preventive programs that overcome the gap between knowledge and safer sexual behaviors in this and similar groups of adolescents and suggest that programs that heighten personal concerns may be most effective. Community-based physicians who care for adolescents should develop such preventive programs and integrate them into their practices.