Sclerosing bone dysplasias are a poorly understood group of developmental anomalies, much of whose etiology is still obscure. The list of conditions constituting this group is relatively short: osteopetrosis (Albers-Schönberg disease), pycnodysostosis (Maroteaux-Lamy disease), enostosis (bone island), osteopoikilosis, osteopathia striata (Voorhoeve disease), progressive diaphyseal dysplasia (Camurati-Engelmann disease), hereditary multiple diaphyseal sclerosis (Ribbing disease), four types of endosteal hyperostosis (van Buchem disease, Worth disease, Nakamura disease, and Truswell-Hansen disease), dysosteosclerosis, metaphyseal dysplasia (Pyle's disease), craniometaphyseal dysplasia, melorheostosis (Leri disease), and craniodiaphyseal dysplasia. There are instances in which two or more of the above disorders coexist. These are termed "overlap syndromes", most commonly involving osteopathia striata, osteopoikilosis, and melorheostosis. A classification of these dysplasias is elaborated based on a targetsite approach that views them as disturbances in development associated with the processes of either endochondral or intramembranous bone formation, or both. Accumulated evidence suggests that many of these disorders stem from common defects in bone resorption and/or formation during the processes of skeletal maturation and modeling. Finally, the subgroup of overlap syndromes is emphasized as indicating a strong interrelationship between the sclerosing dysplasias of bone, with perhaps a common pathogenesis for many.