Osteoporosis and related fractures are a major public health concern globally, and the incidence and subsequent morbidity, mortality and health care costs are expected to increase dramatically over the coming decades. Although osteoporosis was once considered (primarily) a disease of the elderly, there is now universal agreement that the condition has pediatric antecedents. Although genetic factors play an important role in the attainment of an optimal adult (peak) bone mass and strength, lifestyle factors such as physical activity and nutrition are also important determinants of children's bone development. However, there is still much research needed to identify the exact role of modifiable lifestyle factors and childhood illness on long-term adult bone health and fracture risk. Much of our current knowledge is based on bone mineral content and areal bone mineral density assessed by dual-energy X-ray absorptiometry; but with rapidly advancing technology, researchers will be able to more accurately assess other indices of bone strength, such as the material and structural properties of bone, during the growing years. Based on our current knowledge, however, it is clear that intervention strategies aimed at reducing the incidence of osteoporosis must begin in childhood or adolescence if they are to have maximal effect.