The purpose of this chapter is to provide an approach to the diagnosis and treatment of pediatric osteoporosis. Osteoporosis is defined in adults as low bone mineral mass and deterioration of bone micro architecture, with an increased risk of fragility (a traumatic) fractures. It is preceded by a less severe condition named osteopenia (scarcity of bone), the simple reduction of bone mass for gender and age. Osteoporosis is the most common metabolic bone disorder in adults, and remains a major health problem worldwide. There is increasing awareness that osteoporosis may also affect children and adolescents, either because of intrinsic skeletal defects (primary osteoporosis) or as a complication of other diseases or their treatment (secondary osteoporosis). Various methods have been employed to assess bone health in children and adolescents. Evaluation of bone pain and mobility, and x-ray confirmation of fractures are often the first diagnostic step. Low bone mass or osteoporosis are detected by bone densitometry, quantitative computed tomography, peripheral quantitative computed tomography, quantitative ultrasound and, in special cases, bone histology/histomorphometry. The assessment of the basic bone metabolism parameters, such as serum/ urinary levels of calcium, phosphate, vitamin D, parathyroid hormone, is a useful diagnostic complement, while that of bone turnover markers can be useful in special conditions.