Rickets is characterized by impaired mineralization and ossification of the growth plates of growing children caused by a variety of disorders, the most frequent of which is nutritional deficiency of vitamin D. Despite ample knowledge of its etiology and the availability of cost-effective methods of preventing it, vitamin D deficiency rickets remains a significant problem in developing and developed countries. This two-part review covers the history, etiology, pathophysiology and clinical and radiographical findings of vitamin D deficiency rickets. Other less frequent causes of rickets and some of the disorders entering into the differential diagnoses of rickets are also considered. Controversial issues surrounding vitamin D deficiency include determination of what constitutes vitamin D sufficiency and the potential relationship between low levels of vitamin D metabolites in many individuals and unexplained fractures in infants.