Health-related attitudes and behaviours begin to develop early in infancy under different influences. In this study an attempt to establish them, and how different influences are changing during the school years was made. Proceeding from Ajzen's model of planned behaviour, and from other health related theories, a questionary was made and applied to school youth of different age. Four groups of pupils participated in this study, namely 60 fifth grade and 43 seventh grade pupils from primary school, and 54 first grade and 44 third grade pupils from secondary school. With age health concern, motivation to avoid unhealthy behaviour and motivation for health diminish. At the same time disease ignorance and quitting healthy leisure activities increase. Also the decrease of perceived importance of health risk factors can be observed.