A considerable amount of research into osteoporosis has focused on the management and treatment of bone loss in later life. More recently, a limited amount of research has been directed toward the development of an optimal level of peak bone mass during the adolescent and early adult years. While genetics is a major determinant of bone status, there is considerable evidence that physical activity is an important nonhereditary factor. Studies on adults suggest that the positive effect of physical activity on bone is modest in the short term but may be quite powerful with more intense activity that overloads the muscular system for a longer time period. In children, however, our knowledge about the long-term effects of physical activity on bone accretion is incomplete. This paper presents a review of the pediatric literature dealing with the relationship of physical activity to bone mineral density status in the adolescent population.