Tobacco- and alcohol-related behaviors are important public health problems under the sanitary, economic and political point of view; even if the negative consequences of these substances' use and abuse are clear and well recognized, the prevalence of the phenomenon remains however high. Therefore to put in action prevention effective procedures, it is useful to know causes and consequences of the behaviour, but also to be able to quantify them and follow them up. This research is aimed at assessing the spread of tobacco's and alcohol's consumptions among students attending high school in Lodi and Milano (City and Province) during school year 2002-2003 and allows to compare these data with those obtained through a similar study carried out during school year 2000-2001. Data have been collected using a translated and adapted version of the YRBSS questionnaire implemented by CDC to monitor the prevalence of high-risk behaviors among U.S. teens. Tobacco habits appears still high but have not increased in the considered period, while alcohol-related behaviors are growing in popularity and performed by a greater number of adolescents,compared with what happened three years earlier This proves to be particolarly true for girls. Prevention implications are presented on the basis of these results.