OBJECTIVE: This investigation sought to study the influence exerted by demographic and socioeconomic factors on the prevalence of infection in adolescents living in Switzerland. DESIGN: Epidemiological study spanning 3 years. METHODS: We included 196 15- to 16-year-old adolescents from a north-eastern Swiss city in our study, recruited by the school health service during a medical check-up in the years 1999, 2000 and 2001. infection was detected by ELISA using 2nd generation anti- IgG antibodies. Demographic and socioeconomic data were collected by questionnaire. RESULTS: infection was found in 19 of the 196 (9.7%) tested adolescents. tested positive in, respectively, 13 (7.3%) of the 176 natives and six (30%) of the 20 (P = 0.01 chi-squared) subjects from foreign countries. infection was significantly highly correlated with demographic factors but did not correlate with most of the socioeconomic factors. CONCLUSION: The rate of infection among Swiss adolescents is one of the lowest in Europe. Nevertheless, an important disparity is evident between the rate of infection observed in the native population and that among immigrants. High living standards available to the majority of the population may explain the minor influence of socioeconomic factors on infection in our country.