Background: Sexual behavior in young people is influenced by external factors that may increase their vulnerability. Objective: to describe sexual behavior and other indicators of sexual and reproductive health among young people (16 to 24 years) in Catalonia and to identify factors associated with sexual risk behaviors. Methods: Cross-sectional study in 2012 carried out by an online survey from a panel of population (n=800). Factors associated with not using a condom at last sexual intercourse were evaluated using multivariate logistic regression models. Results: 76.1% of boys and 83.3% of girls reported having had complete sexual intercourse (p=0.012). The proportion of boys and girls who reported casual partners was 39.7% and 22.5%, respectively. 31.4% of boys and 10.3% of girls reported having contacted partners through Internet. Not using a condom at first sexual intercourse showed significant association with reporting not using a condom in the last sexual intercourse, for both, boys (OR=2.50) and girls (OR=3.18). Having contacted partners through the Internet (OR=2.29) was associated with this risky sexual behavior in boys, and having used the emergency contraception 3 or more times (OR=3.38) was associated in girls. Conclusions: There are differences in the sexual behavior of young people by sex, being condom use at first sexual relationship a good predictor of condom use at last sexual intercourse. Boys show a higher number of casual partners than girls, as well as a higher use of the Internet to contact sexual partners.