The evaluation of puberty in this project will follow exactly the protocol of the BMDCS project. The impact of pubertal stage on bone mineral accrual will be explained to all participants at the entry study visit, so that they and their families will understand the purpose of the physical examination for pubertal status. The pediatric endocrinologist (MH), following the protocol established for the multicenter BMDCS project, will evaluate pubertal stage. For girls, breast development will be assessed by visual criteria, but also by palpation in the earliest stages of puberty (Marshall and Tanner 1971, Biro 1992). For boys, testicular size will be assessed using the ovoids of the Prader orchidometer (Zachman 1974, Biro 1995). For both boys and girls, pubic hair development will be assessed by the criteria of Tanner (Marshall and Tanner 1970, 1971).