(1) Cysteamine bitartrate (also known as mercaptamine) is marketed for the treatment of cystinosis, a rare hereditary disease which, in its juvenile and infantile forms, progresses spontaneously to severe renal and ocular impairment, growth retardation with rickets, and involvement of many other organs. Only symptomatic treatments have been available until now. (2) The clinical file includes only non comparative trials. (3) Few children have been treated with cysteamine beyond the age of 10. Provided treatment is begun early, the main beneficial effects of cysteamine are maintenance of the growth curve and prevention of deterioration of renal lesions (an effect that varies from patient to patient). Oral cysteamine does not prevent the progression of ocular lesions. (4) Cysteamine has many potential adverse effects, some of which are serious (mainly gastrointestinal and neuropsychiatric disorders). Little is known of its long-term adverse effects. (5) The main disadvantage of this treatment is the need for four daily intakes (every 6 hours) and the sulphurous breath it causes. (6) Treatment with cysteamine is expensive.