A study of 4,976 high-school students in Israel, representative of this age group for the entire country except for 13 percent who attend religious schools, revealed that about one-third of the boys aged 14-15 and almost one-half of those in the 16-17 age category have had sexual intercourse. The respective figures for girls are 6 percent and 16 percent. Age at onset of sexual activity was found to be higher and the level of knowledge about the same as in reports from the Western world. Students of Oriental origin, as well as those considering themselves religious or traditional tended to be less active sexually, more conservative in their attitudes, and less knowledgeable. In contrast, students of both sexes residing in kibbutzim were found to be more active sexually and more knowledgeable. A double standard for girls was accepted, especially among the female respondents, except in the kibbutzim. A subgroup of girls highly sexually active, in contrast to their own attitudes, has been identified, and possible reasons for this discordance discussed. As sexual activity among teenagers is becoming more prevalent, comprehensive and early sex education school programs should be encouraged.