Although they are individually rare, many unusual disorders of skeletal formation and homeostasis exist.1,2,3,4,5,6 and 7 Some entities are mere radiographic curiosities; others are lethal. Some are associated with well-defined endocrine or metabolic abnormalities, and the endocrinologist may be consulted for his or her expertise, especially regarding metabolic bone disease. Cumulatively, the number of affected individuals is significant. Accordingly, this chapter provides a review of several of these conditions.