We report an 18-month-old girl who presented in chronic renal failure after an illness characterised by protracted diarrhoea, poor weight gain and anaemia. There were no symptoms and signs suggestive of a renal Fanconi syndrome, but a diagnosis of nephropathic cystinosis was suggested by renal biopsy and confirmed by an elevated leucocyte cystine concentration. We suggest that the diagnosis of cystinosis should be considered in any child with chronic renal failure of unknown aetiology.