To assess developmental differences in the psychological functioning, substance use, coping style, social support, HIV knowledge, and risky sexual behavior of at-risk, minority adolescent girls; to assess developmental differences in psychosocial correlates of risky sexual behavior in older and younger adolescents. Participants included 164 minority teens, ages 12-19, who were receiving medical care in an adolescent primary care clinic. Teens completed measures of psychological adjustment, substance use, coping style, social support, religious involvement, and HIV knowledge and attitudes. In addition, they answered questions regarding their sexual history, family situation, school status, and psychiatric and legal history. Younger teens (ages 12-15) reported more symptoms of depression and earlier sexual debuts than older teens (ages 16-19). However, older teens reported significantly more substance use and were more likely to have been pregnant and to have contracted a sexually transmitted disease (STD) than younger teens. Older teens also reported more religious involvement and using more adaptive coping strategies than younger teens. Developmental differences in the correlates of risky behaviors were also found between younger and older teens. Specifically, conduct problems and substance use were significantly associated with risky sexual behavior for younger teens, but not for older teens. Similarly, younger teens whose peers were engaging in risky behaviors reported engaging in more risky sexual behaviors; however, these same relations were not found for older teens. Young minority adolescents exhibiting conduct problems and using substances seem to be at highest risk for contracting HIV and STDs as a result of risky sexual behavior. Prevention interventions should target teens in high-risk environments during late elementary school or early middle school to encourage teens to delay intercourse, practice safer sex, and avoid drug and alcohol use. An interdisciplinary model of care in primary care settings is clearly indicated to provide these services to at-risk youths.