Cystinuria is a complex hereditary disorder that affects both sexes with equal frequency and severity. Symptoms usually begin early (children and young adults) but may develop at any age. Stature is normal and there are no clinical nutritional abnormalities. The morbidity of cystine urolithiasis is considerable. Hyperuricemia is a frequent associated finding and is probably the result of multiple factors. No other abnormalities are consistently related to this disease. Treatment with adequate oral fluids to ensure a copious urine volume and with oral alkali to keep the urine alkaline is most successful when used prophylactically in the stone-free patient. However, dissolution of existing calculi is unlikely with this regimen alone. The addition of D-penicillamine often results in dissolution of stones and prevention of recurrent calculi in patients who have continued stone growth despite the use of oral fluids and alkali. Because toxic reactions with D-penicillamine are frequent and sometimes severe, this drug should be used only when necessary and then as an adjunct to rather than a substitute for increased oral fluids and alkali. Failure of treatment in spite of adequate therapy should alert the physician to the possibility of coexisting complicating problem.