PURPOSE: To investigate sexual behavior and attitudes toward sexuality among first-year high school students in Sweden in 1999 and to compare the sexual behavior with that reported from similar studies in 1979 and 1989. METHODS: In Spring 1999, a questionnaire with 47 questions mainly of multiple-choice nature was administered to a random sample of 20 classes in senior high school in two medium-sized cities in Sweden. The median age of the students was 16 years. Differences in sexual behavior and attitudes were evaluated with the Chi-square and Student's t-test. RESULTS: Almost half of the students (46%) had had intercourse, showing that the age of coitarche had not decreased during the past two decades. The median age at intercourse of those who had had intercourse was 15 years in both genders. More students in practical (vocational-technical) programs (60%) than in theoretical (college preparatory) ones (37%) had had sexual intercourse. More teenagers in theoretical (90%) than in practical programs (64%) had used contraceptives at their first intercourse, an increase from 65% in 1979 to 76% in 1999. One-fourth of the teenagers were under the influence of alcohol at the first intercourse, a decrease, compared with 1979. CONCLUSIONS: Contraceptive use at coitarche has increased and alcohol use decreased over the 20-year-period. The tendency noted 10 years ago that students attending practical programs put themselves at more health risk than students in theoretical programs continues. This fact should be considered when planning for counseling and sex education.