To report new adverse effects of cysteamine.Detailed clinical information was obtained from the patients' physicians.New adverse events were reported in 8 of 550 patients with cystinosis treated with cysteamine in Europe during the last 5 years. Detailed clinical information was not available for 2 of these patients, 1 of whom died from cerebral ischemia. The 6 evaluable patients developed vascular elbow lesions (6/6), neurologic symptoms (1/6), bone and muscle pain (2/6), and/or skin striae (2/6). Analysis of biopsy specimens from the elbow lesions demonstrated angioendotheliomatosis with irregular collagen fibers. In 3 of the 6 patients, the daily cysteamine dose exceeded the recommended maximum of 1.95 g/m(2)/day. Dose reduction led to improvement of signs and symptoms in all 6 patients, suggesting a causal relationship with cysteamine administration.Cysteamine administration can be complicated by the development of skin, vascular, neurologic, muscular, and bone lesions. These lesions improve after cysteamine dose reduction. Doses >1.95 g/m(2)/day should be prescribed with great caution, but underdosing is not advocated.