A 14-year-old boy presented with the clinical and radiological features of rickets. Serum inorganic phosphate levels were constantly low, whereas serum calcium and parathyroid hormone levels were within the normal range. Laboratory investigation did not show any evidence for vitamin-D deficiency, chronic renal insufficiency, Fanconi syndrome, tubular acidosis, hepatic disease or intestinal malabsorption. A family study comprising 34 members over four generations revealed 10 other individuals to be affected and the mode of inheritance to be autosomal dominant. In addition to hypophosphataemia and normocalcaemia, the disease is characterized by elevated serum 1,25 dihydroxyvitamin D levels and hypercalciuria. This hereditary syndrome of renal hypophosphataemia differs from the common familial X-linked hypophosphataemia and the recently described autosomal recessive hypophosphataemic rickets with hypercalciuria by its dominant mode of inheritance; it differs from hypophosphataemic non-rachitic bone disease by the elevated serum 1,25 dihydroxyvitamin D levels and hypercalciuria.