Large-scale, national surveys to assess smoking and use of alcohol among representative samples of Norwegian school children were conducted in November 1983, 1985, and 1989. The surveys were part of the international WHO-study: Health Behaviour in Schoolchildren. A total of 3,391 (1983), 3,955 (1985) and 5,037 (1989) 5th, 7th and 9th grade students completed an anonymous questionnaire. The results clearly show that both experimentation and regular use of cigarettes and alcohol take place as early as in the 5th grade. There is a strong increase in reported use from the 5th to the 9th grade. In 1989, by the time they reached the 9th grade the large majority of students had tried smoking at least one cigarette (60% of the boys and 58% of the girls) or had tried drinking alcohol (85% of the boys and 80% of the girls). Furthermore, a substantial proportion of the students reported regular use of these substances. In 1989, 22% of the 9th grade boys and girls reported smoking every day or every week. Similarly, 29% of the boys and 27% of the girls reported drinking alcoholic beverages at least once a month. Comparing the results across the three surveys, we find that an encouraging decline in self-reported use of cigarettes and alcohol seems to have taken place from 1983 to 1989 among school children 11-16 years old.