Osteoporosis is not only a major public health problem in the adult population but is increasingly diagnosed during childhood. Most cases are secondary to chronic illnesses (secondary osteoporosis). In chronically ill children several factors, in addition to the underlying chronic illness itself, may predispose to either reduced bone mass or impairment of bone quality. Osteoporosis in the otherwise healthy child (primary osteoporosis) is generally classified as either osteogenesis imperfecta (OI) or juvenile idiopathic osteoporosis (JIO).