The psychosocial and intellectual development of 12 children with infantile nephropathic cystinosis was investigated longitudinally by use of biographical data, long-term behavioral observations and psychological assessment. Of the 12 patients, eleven suffered terminal renal failure and 7 of these were followed up after renal transplantation. In spite of the severe illness and the resulting unusual life conditions the patients showed normal intellectual capacity and most of them average school performance. The patients were socially adapted, their behavior was predominantly cooperative, shy and reserved, but depressive at times. After transplantation the children became more active and outgoing. However, growing discrepancies between their physical development and their emotional and social age may lead to adaptational problems at adolescence which may require psychological counselling.