The calcium requirements of boys and girls during adolescence have largely been based on balance studies, including more recently the use of stable nuclides. Bone measurements by dual energy X-ray absorptiometry (DXA) and similar instruments have provided an end-point by which to assess skeletal development, either of the entire skeleton or of specific bones, in relation to the consumption of calcium and other nutrients and to physical activity. Several cross-sectional studies, using measurements of bone mineral density (BMD) and bone mineral content (BMC), suggest that optimal calcium intakes for female adolescents may be somewhat lower than published as the Adequate Intakes (AIs) by the Institute of Medicine in 1997, but they may be somewhat higher for adolescent males. These results suggest that gender should be considered in establishing recommendations for calcium. In addition, other studies have provided evidence that prepubertal and postpubertal skeletal growth of males and females is enhanced by regular physical activities and that the optimal attainment of BMC and BMD by females by late adolescence may not be dependent on such a high calcium intake as previously thought, although males may need at least the recommended amount. Therefore, physical activity should also be considered in establishing recommendations for calcium. In summary, two lines of evidence suggest that more extensive information on diet and lifestyle should be considered in the future for making more specific recommendations on calcium intakes for optimal skeletal development for prepubertal and postpubertal boys and girls.