The purpose of the study was to test a biopsychosocial process model based on theoretically and empirically supported factors previously found to influence health and complaints in children and adolescents. Participants (N = 823) of the ages of nine, 14 or 18 were administered parts of the Health Behaviour in School-Aged Children Questionnaire and a physical activity questionnaire. They subsequently underwent physical fitness tests and a medical examination. For complaints, direct and indirect influences over four levels (socioeconomic status, physical activity of relatives and peers, physical activity and physical fitness) were shown, but the findings did not hold for health. The interpretation of expected and unexpected results is discussed.