Males who had had a girlfriend their age by seventh grade were more likely than those who had had no relationship to report sexual activity in ninth grade (odds ratio, 2.1). Similarly, for females, the odds of being sexually active in ninth grade were elevated among those who had had a boyfriend their age (2.9); however, they also were higher among those who had had an older boyfriend than among those who had had one their age (2.1). With sixth-grade risk factors controlled, relationship status in seventh grade remained significant only for females; the association was explained by early menarche and by participation in situations that could lead to sex and riskier peer norms in eighth grade. For males, eighth-grade situations that could lead to sex, Hispanic ethnicity and sixth-grade peer norms explained ninth-grade sexual behavior.