Two elderly patients presented with renal failure due to pelviureteric junction (PUJ) obstruction. After dialysis, obstruction was relieved by percutaneous nephrostomy and the diagnosis was established radiologically. Differential renal function was assessed by direct measurement or isotope scanning. Surgical correction resulted in both patients remaining free of dialysis at follow-up 2 years later. PUJ obstruction is an uncommon cause of renal failure, particularly in the elderly, but is potentially correctable.