Although young sexually active adolescents are at greater risk for human immunodeficiency virus (HIV) acquisition than their abstinent peers, little is known about their respective HIV-related knowledge, attitudes, and general risk behaviors. This study of middle school adolescents (n = 1379; mean age, 13.2 years) found that the sexually active boys, compared with their peers, were less knowledgeable about HIV, less fearful of HIV, less tolerant of people with acquired immunodeficiency syndrome (AIDS), riskier in non-HIV-related attitudes and had a greater history of other risk behavior. A similar, but less marked pattern, was found for girls. It is suggested that physicians counsel all adolescents about HIV and sexuality during office visits and that early adolescent sexuality should prompt special efforts in HIV education/counseling.