Osteopetrosis is a hereditary disorder in which pathologic alteration of osteoclast resorption of bone results in thickening of cortical and lamellar bone. Before bone marrow transplantation, the infantile recessive form was uniformly fatal within the first two decades of life as a result of invasion of the marrow space by abnormal bone formation. The adult autosomal dominant form causes minimal morbidity and is usually diagnosed incidentally on routine radiographs. Although osteopetrosis is an extremely rare disorder, the study of this disease can provide insights into the formation of bone and the inheritance of disease.