Infantile cystinosis is a metabolic lysosomal storage disease of cystine affecting most of the body cells. The first symptoms appear after 5-6 months of life: anorexia, vomiting, polyuria, polydipsia and failure to thrive, associated with the signs of tubular Fanconi syndrome including glycosuria, proteinuria, loss of bicarbonate, phosphate, potassium, sodium, etc. Treatment with cysteamine is effective if started as early as possible. This treatment delays or prevents the spontaneous evolution toward end-stage renal failure, usually between 6 and 12 years of age, and also prevents growth stunting. In the long term, other organs may be involved like eye, thyroid, endocrine pancreas, muscle and central nervous system. The diagnosis is ascertained by leucocytes cystine assay, also useful for the follow up and the adjustment of the treatment. Prenatal diagnosis is available on chorionic sample. The gene of the disease is not yet identified but is known to map to chromosome 17.