This chapter presents certain definitions and disorders related to high bone mass such as deformity, dysostosis, dysplasia, and hyperostosis. The malformation of one or a few individual bones is called as "dysostosis." The heritable and symmetric imperfect development of the skeleton leads to dysplasia. The disorders that cause high bone mass mainly by dysplasias and dysostoses include: autosomal dominant osteosclerosis, frontometaphyseal dysplasia, central osteosclerosis with ectodermal dysplasia, and osteoporosis. The metabolic disorders are also mentioned- namely, carbonic anhydrase II deficiency, fluorosis, heavy metal poisoning, and hepatitis C associated osteosclerosis, and so on. There are certain other disorders that are taken into account- leukemia. Lymphoma, mastocytosis, and multiple myeloma are also discussed in the chapter. The radiographic patterns of high bone mass can be done by three methods- namely, cortical and trabecular bone, cortical bone, and trabecular bone depending on the disorder respectively.