Abstract The purpose of this study was to compare the sexual behavior of Swedish teenagers in the late 1980s with that in the late 1970s, when a similar study was performed in the same city. Another aim was to discover differences between boys and girls, smokers and nonsmokers, and pupils in theoretical and practical classes. A total of 383 high-school students answered a questionnaire about their sexual behavior, education, and attitudes. Almost one-half of the teenagers had already had intercourse. The median age at sexual debut was about 17 years. Among girls who had had intercourse, the median age at debut was lower than 10 years ago. A majority stated that their sexual behavior had been affected by the acquired immunodeficiency syndrome (AIDS) debate. This was, however, not clearly seen in their sexual behavior. Intercourse seemed to take place earlier in the relationship than 10 years ago, and the wish for more sexual experience had increased. The use of alcohol at the time of first intercourse had decreased significantly. Only 2% thought that they had too much sex education at school. As many as 41% felt they could not talk about sex with their parents. Efforts should be made both to enhance the quantity of sex education at school and to improve its quality. This might increase the chances of young people avoiding unwanted pregnancies and sexually transmitted diseases.