The purpose of this study was to increase understanding of the prerequisites for tobacco prevention. The situations before and after the introduction of a minimum-age law were compared with respect to opportunities for adolescents to buy tobacco, and to attitudes towards the law. Data were collected in 1996 and 2000 with a questionnaire among all pupils in years 7 and 9 of compulsory school, and among pupils in year 2 of upper-secondary school in three regions of Sweden. Tobacco had become less available from shops, while there was an increase in the proportion of adolescents who buy tobacco from friends. Among smokers the support for this law was higher in 2000 than 1996, while the pattern among non-smokers was not consistent across age-groups or gender. Regardless of smoking habits, age-group and gender, the proportion of adolescents who believed that the law had an effect in reducing smoking had decreased. The changes described in this article are discussed in terms of the different ways available to improve the implementation of the minimum-age law.