A case of primary hyperparathyroidism with clinical signs of rickets in a 15-year-old boy of South Morocco is presented. X-ray findings include a diffusely osteoporotic skeleton with areas of subperiostal resorption, cysts and metaphyseal rachitic changes. Hypercalcaemia, hypophosphataemia, increased alkaline phosphatase are found together with low calcidiol and high calcitriol plasma levels. The surgical removal of a chief-cell adenoma of a parathyroid gland leads to very rapid bone healing as well as normalization of blood chemistry. Reviewing the literature shows that 10 similar cases have been described. However, no correlation can be established between the occurrence of rachitic lesions and the Ca X P product. When limited calcium is available from the gut, elevated calcitriol then contributes to mobilize more mineral from bone, in conjunction with parathormone. In addition, the interaction of these 2 hormones on the renal tubule maintains a phosphate leak, creating proper conditions for the development of rachitic lesions.