A total of 111 adults with malignant disease of the bladder were studied to determine the long term complications of ileal conduit diversion. Each patient had survived at least five years (mean 10 years) after cystectomy. At final follow up the radiological appearance of one or both kidneys had deteriorated in 50 (47%) of 107 patients: deterioration worsened significantly (p less than 0.01) with increasing duration of follow up. Eighteen patients (16%) developed biochemical evidence of impaired renal function, of whom four died of complications of renal failure. Bilateral upper tract dilatation was noted in 30 patients (28%), and in 21 its cause was obscure. Ten patients formed renal stones, and an additional 12 required further operations on the conduit or stoma. Despite the age of patients with bladder cancer and the poor prognosis of those with invasive tumours clinically important side effects were observed in a significant proportion of the long term survivors. Further efforts to determine the aetiology of upper tract dilatation in patients with an ileal conduit diversion are justified.