BACKGROUND: Despite the relevance of this research topic from a public health perspective, there is currently a lack of objective data on the frequency and context of European adolescents' sport activity, their motivations to engage in sports, as well as the links between their sport habits and their health attitudes and behaviors. OBJECTIVES: 1) to describe the sport habits of adolescents in Switzerland and their motivations to get involved in a physical activity, 2) to define the sociodemographic profile of adolescents defined as athletic, 3) to determine the nature of the associations between the frequency of sport activity and health variables. METHOD: In the 1993 Swiss Multicentric Adolescent Survey on Health, anonymous self-administered questionnaires were distributed to a national representative sample of 10,000 in-school adolescents (15 to 20 years old). The answers were investigated by means of univariate analyses. RESULTS: Half of the sample do sports more than twice a week, boys more often as part of a sports club. Motivations depend on the gender, girls doing sports for self image and health motivations and boys for competition and relational reasons. Almost all the sociodemographic characteristics show statistically significant differences between "non athletic", "fairly athletic" and "athletic" adolescents, which suggests the influence of the sociocultural background on the perception of sport activity. These three groups also differ as regards their health behaviors, attitudes and perceptions; the most athletic adolescents generally give more positive answers in terms of prevention and perceived health. These findings have implications for health promotion, notably as regards the creation of the material conditions more likely to favor adolescents' involvement in physical activity.