Background. In this study the effect is assessed of (repeated) well-care visits and freely accessible consultation hours at secondary schools on the prevalence of adolescent health-comprising behaviour and later obesity. Method. An ecological case-referent study design was used with data from the Netherlands Bureau of Statistics, the Ministry of Defence, the 1992 High-School Student Study, all youth health care departments in The Netherlands and relevant census. Data from the High-School Student Study included 4569 students aged 12-18 years, of whom 4167 had answered all questions on health-comprising behaviour and eating habits. The data from the Ministry of Defence included 1004 cases with a body mass index greater than 27 of a total of 12 251 male conscripts. The census of 18- and 19-year-old males in the regions of the relevant youth health care departments served as referents. Results. Except for the use of alcohol, the effect of more well-care visits was in all cases negative, and for the use of tobacco even significantly so [odds ratio (OR) = 1.15, 95 per cent confidence interval (CI) = 1.01-1.33]. The availability of open consultation hours had an adverse effect on use of alcohol (OR = 1.29, 95 per cent CI = 1.11-1.50). The OR for obesity in male conscripts showed an adverse effect of a greater number of well-care visits (OR = 2.46, 95 per cent CI = 1.74-3.46) and the availability of open consultation hours (OR = 1.97, 95 per cent CI = 1.72-2.25). Conclusion. This study does not support the hypothesis that, at a population level, preventive activities of youth health care departments such as (more) frequent well-care visits or offering open consultation hours at secondary schools, have a beneficial effect on prevention of health-comprising behaviour or obesity.