The term "vitamin D-dependent rickets" describes a group of genetic disorders characterized by earlyonset rickets due to the inability to maintain adequate active vitamin D levels or the inability to respond adequately. with activated vitamin D. Although the term is now recognized as a pathophysiological misnomer, there is clinical relevance to its continued use, as the patient must be "dependent" for life on the use of a specialized vitamin D replacement regimen . This review examines the molecular basis of the three forms of vitamin D-dependent rickets and summarizes current regimens for the management of affected individuals.