RESUMO
A study of sexual behavior among teenagers was carried out in a random sample of 884 second degree school (high school) students of Porto Alegre (South Brazil) by means of a self-report questionnaire. The students' ages ranged from 13 to 22 years old, and 59% of them were females. The students believed themselves well-informed about physiologic phenomena involved in human reproduction (95.2%; 95% confidence interval (CI):93.5-96.5) and sexually transmitted diseases (STD) (82.1%; 95% CI:79.1-84.7). In addition, 42.4% (95% CI:39.0-45.8) said that they has had a sexual relationship. However, 51.5% (95% CI:45.9-57.0) did not use contraceptive precautions systematically, and 12% (95% CI:7.2-19.0) of girls had already undergone an abortion. Considering these results, it is important to stimulate programs for sexual education strictly focused on teenagers.