Sclerosing bone dysplasias are a group of unusual disorders with important and frequently lethal complications. During the past 8 years more than 80 patients with disorders of this type have been investigated in the Department of Human Genetics, University of Cape Town. It has emerged that a condition in this category 'sclerosteosis', has a high prevalence in individuals of Afrikaner stock and more than 40 affected patients have been studied. Other conditions which have been investigated during this survey include various types of osteopetrosis, pycnodysostosis and craniometaphyseal dysplasia. In each, specific radiographic features facilitate the diagnostic precision which is crucial for effective prognostication and management. Orthopaedic complications are an important aspect of these disorders.