The de Toni-Fanconi syndrome* is a clinical constellation characterized by resistant rickets, acidosis, glycosuria, hyperamino-aciduria, and organic aciduria. This syndrome belongs to a group of diseases based on abnormalities in renal tubular function. The renal abnormality in patients with the Fanconi syndrome consists of a deficient tubular reabsorption of phosphorus, amino acids and glucose along with a deficiency in the tubular mechanism for reabsorbing base without acid. In a number of children having clinical evidence of the Fanconi syndrome, postmortem histological studies have revealed deposits of cystine crystals scattered throughout various organs and tissues of the body, particularly in the reticuloendothelial system. In recent years an increasing number of instances have been reported in which cystinosis has been detected ante mortem by examination of bone marrow aspirates or by a slit-lamp examination of the cornea of the eye. In Table 1 are tabulated a number of cases1-55 which have