Findings show that higher levels of childhood antisocial behavior between 5 and 11 years old were associated with an increased likelihood of early sexual initiation and high-risk sexual behavior by age 21 years. In contrast, childhood hyperactivity was unrelated to any of the sexual outcomes measured. Higher levels of childhood anxiety were associated with a significant decrease in the likelihood of engaging in risky sexual behavior and in contracting sexually transmitted infections by age 21. The lowest level of childhood anxiety was associated with the greatest risk for subsequent risky sexual behavior and the acquisition of sexually transmitted infections. This association between level of childhood anxiety and later risky sexual behaviors suggests that childhood anxiety level is related to level of behavioral restraint and the level of willingness to engage in risky behaviors. Participants were enrolled in the Dunedin Multidisciplinary Health and Development Study (n=1,037), a prospective longitudinal study of a New Zealand birth cohort born in 1972-73. Data were collected at ages 5, 7, 9, 11, 13, 15, and 21 years. Adjustment was made for gender, socioeconomic status, parenting factors, and residence changes. For assessments of childhood behavior at ages 5, 7, 9, and 11, parents and teachers were asked to complete the Rutter Child Scales. Sexual behavior was assessed at age 21 years with a questionnaire based on the 1990 British National Survey of Sexual Attitudes and Lifestyles. The following measures were used to assess sexual health outcomes. Early sexual intercourse, having sexual intercourse with three or more different partners in the past year, and "never or only sometimes" using a condom were measures of risky sexual behavior. After being given definitions of various sexually transmitted diseases, participants were asked about being infected with them. 2 tables and 40 references