The North Karelia Youth Project is based on the results of previous pilot studies in North Karelia and forms part of the North Karelia integrated programme for non-communicable diseases prevention, co-ordinated by the WHO and conducted by the Finnish National Public Health Institute. The project is designed to test the feasibility and effects of a largescale health programme among 12–16 year old schoolchildren. The educational programme aims to prevent cigarette smoking and alcohol use mainly by training pupils to resist social pressures and by modifying perceived social norms which may lead to smoking and alcohol use. The dietary intervention aims to improve dietary habits to decrease serum cholesterol and blood pressure level. The programme also aims to promote positive decision-making and coping skills and to increase social support for coping with stress. The study, which began in the autumn of 1984 provides a comprehensive three-year programme for all seventh graders (ages 12–13) and succeeding age cohorts in North Karelia (24 schools) and in selected schools in the county of Kuopio (eight schools), including approximately 4 000 students in the first year and 12 000 over the entire study period. Simultaneously successive measurements are implemented in all the intervention schools and in eight randomized reference schools, which will allow us to evaluate the programme and to test a number of hypotheses about programme effects. The preventive programme is designed to make the best possible use of existing resources (teachers, parents, community) and will require only relatively modest new expenditure so that, if proved effective, it can be continued on a permanent basis. A baseline survey of the schools was carried out in the spring of 1984 among ninth-graders. Twenty-four per cent of the boys and 18% of the girls reported smoking daily and 13% and 9% respectively were occasional smokers. About 20% had used alcohol during the past week, 7% reported “passing out” because of drinking during the last year and 12% had been deeply drunk. The mean serum cholestrol level was 4.7 mmol/l and the mean blood pressure 130/66 mmHg. At this baseline survey, the levels of these variables were generally comparable in the different randomly assigned study groups, although there was a trend towards less smoking and alcohol use at baseline in the schools in North Karelia than in those in the county of Kuopio.