Sixty percent of women and 52 percent of men now in their 20s took a sex education course by age 19, according to the 1984 National Longitudinal Survey of Work Experience of Youth. Whites are more likely than either blacks or Hispanics to have had a course by that age--57 percent compared with 53 percent and 48 percent, respectively. The survey also shows that large proportions of teenagers initiate coitus before they have taken a sex education course. Among young women who first have sex at age 15, for example, only 48 percent have already taken a course (i.e., have taken it at a younger age or at the same age); and among young women who first have intercourse at age 18, the proportion is 61 percent. Young men are even less likely than young women to take a course before they begin coitus--at age 15, the figure is 26 percent, and at age 18, 52 percent. Adolescent women who have previously taken a sex education course are somewhat more likely than those who have not to initiate sexual activity at ages 15 and 16 (though they are no more likely to do so at ages 17 and 18). However, the effect of prior sex education is small, and is weaker than that of virtually every other variable found to have a significant relationship with first intercourse at ages 15-16. Among the strongest determinants of first coitus at those ages are infrequent church attendance, parental education of fewer than 12 years and black race. Older sexually active girls who have previously had a course are significantly more likely to use an effective contraceptive method (73 percent) than are those who have never taken a course (64 percent). This relationship may offset any effect that a sex education course may have in raising the likelihood of early first coitus, since no significant association can be found between taking a sex education course and subsequently becoming premaritally pregnant before age 20.