Background: Influencing adolescents' sexual behaviors has the potential to influence trajectories of risk for sexually transmitted infections (STIs) among young adults. Objective: To determine whether family, school, and individual factors associated with increased duration of virginity also protect against STIs in young adulthood. Design: Prospective cohort study. Wave I of the National Longitudinal Study of Adolescent Health occurred in 1995 when participants were in grades 7 through 12. Six years later, all wave I participants who could be located were invited to participate in wave III and provide a urine specimen for STI testing. Setting: In-home interviews in the continental United States, Alaska, and Hawaii. Participants: Population-based sample. Of 18 924 participants in the nationally representative weighted wave I sample, 14 322 (75.7%) were located and participated in wave III. Test results for Chlamydia trachomatis, Neisseria gonorrhoeae, and Trichomonas vaginalis were available for 11 594 (81.0%) of wave III participants. Main Outcome Measure: Positive test result for C trachomatis, N gonorrhoeae, or T vaginalis. Results: Controlling for biological sex, age, race/ethnicity, family structure, and maternal education, adolescents who perceived that their parents more strongly disapproved of their having sex during adolescence were less likely to have STIs 6 years later (adjusted odds ratio, 0.89; 95% confidence interval, 0.81-0.99). Those with a higher grade point average during adolescence were also less likely to acquire STIs (adjusted odds ratio, 0.84; 95% confidence interval, 0.71-0.99). Stratified analyses confirmed these findings among female, but not male, adolescents. Feelings of connection to family or school, reported importance of religion, attending a parochial school, and pledges of virginity during adolescence did not predict STI status 6 years later. Conclusions: Perceived parental disapproval of sexual intercourse and higher grades in school during adolescence have protective influences on the trajectory of risk for acquiring STIs, primarily among female adolescents. Most factors associated with increased duration of virginity in adolescence do not influence the trajectory of STI risk.