A cohort study on a sample of 327 high school students was carried out between 1983 and 1985. Health and behaviour problems were investigated. During adolescence psychosomatic, depressive and behavioural problems appear to be common. The majority of young people suffer at least one problem at 18 years of age. The type of problems are closely related to gender: among boys behavioural problems (BP), such as alcohol or drug consumption, tobacco smoking and violence, are important; among girls sleep disorders, headaches and depressive symptoms (PDS) are frequent. During adolescence sex differences become clearly established. Between 16 and 18 years of age the average number of behavioural problems rises from 0.5 to 1.5 for boys and remains stable (around 0.5) for girls. During the same period the PDS average rises from 1.6 to 2.0 for girls and remains stable (around 0.7) for boys. Even if there exists a correlation between BP and PDS (this correlation is higher in the early age than later on), one type of problem is always predominant, according to sex. BP as well as PDS are related to the intolerance of frustration. Authors conclude that these problems must be considered as the expression of the inability to metabolize or cope with the conflict.