Numerous research works have been performed following the identification of 1,25-dihydroxyvitamin D in the early 1970s which concern the synthesis and role of this hormonal form of vitamin D, as well as the structure and function of its receptor. At the same time, a peculiar type of rickets resulting from a resistance to this hormone, has been described the so-called "pseudo-deficiency rickets type II". Although exceptional, pseudo-deficiency rickets type II has enabled studies which led to the description of several alterations in the vitamin D receptor chromosomal gene responsible for tissue resistance to 1,25-dihydroxyvitamin D. This article reviews present knowledge on the physiological role of 1,25-dihydroxyvitamin D, the structure and function of is receptor, the pathological consequences of its alteration leading to pseudo-deficiency rickets type II, and the reported therapeutic attempts to cure this form of rickets.