As a part of the large project Cardiovascular Risk in Young Finns, the purpose of the present study was to examine how adult physical activity is influenced by early physical activity and current social and health-related factors. A total of 2411 children and adolescents aged 9, 12, 15 and 18 years were randomly selected from five university towns and their rural surroundings in 1980. They were followed up for 12 years by means of questionnaires. In 1992 they were 21, 24, 27 and 30 years old. The results showed that early physical activity and current social and health-related behaviours were significantly related to the level of adult physical activity. Multivariable analyses indicated that early physical activity, in particular, was the best predictor of adult physical activity in all groups, with the exception of the 21-year-old women. The social and health-related factors such as occupation, employment status and smoking also predicted physical activity in some age-gender groups.