In the current study we examined individual growth curves of frequency of sexual intercourse among a sample of urban, low-income, African American youth at increased risk for subsequent HIV/AIDS exposure. Three waves of longitudinal data from the Collaborative HIV-Prevention Adolescent Mental Health (CHAMP) project were utilized. Participant ages ranged from 9 to 12 years (M = 11 years) at the first interview wave and from 15 to 19 years (M = 18 years) at the final interview wave. As such, we were able to map out true developmental trajectories of sexual intercourse over a 10-year period of adolescence (spanning ages 9 to 19 years). Results indicate that the average study participant was sexually abstinent (in terms of intercourse) during the preteen years, reported a single episode of sexual intercourse between ages 14 and 15, and by age 19, reported between 3 and 10 episodes of sexual intercourse. Significant variability in the acceleration of growth rates (as captured by a quadratic random effect) was observed, suggesting that some youth accelerated more rapidly (in their sexual intercourse histories) than did others. Participant gender predicted trajectory starting points; boys reported higher rates of sexual intercourse at age 12. Frequency of baseline exposure to sexual possibility situations (i.e., being in mixed-sex company in a private place in the absence of adult supervision) predicted growth curve acceleration, suggesting preteens with more exposure to sexual possibility situations accelerated more rapidly in their rates of sexual intercourse over time. Developmental implications of these data are discussed.