The purpose of this study was to determine if physical activity, aerobic fitness and isometric strength during adolescence were predictors of cardiovascular risk factor levels in young adulthood. The following measurements were carried out: maximal oxygen uptake (VO(2)max), maximal voluntary contraction (MVC) in four muscle groups, physical activity (questionnaire), blood pressure (BP), total cholesterol, high density lipoprotein cholesterol (HDL-C), triglycerides, anthropometric variables and body fat % (sum of four skinfolds). The data were collected from the Danish Youth and Sports study, an observational longitudinal study in which two measurements were carried out over an eight-year period. The findings in this study indicated that the relationships between the absolute levels of physical fitness and activity in adolescence and the subsequent level of CVD risk factors are weak. However, the changes in physical fitness and physical activity were related to the absolute levels of CVD risk factors in young adulthood, especially in men. Weak relationships were found between the changes in physical fitness/activity and changes in CVD risk factor levels in both sexes. In conclusion, many subjects changed their levels of physical activity and physical fitness between adolescence and young adulthood and the changes, especially in aerobic fitness, seemed to be the best predictor of CVD risk factor levels in young adulthood.