A 74-year-old man with metastatic prostatic carcinoma developed acute oliguric renal failure, a microangiopathic haemolytic anaemia and thrombocytopaenia. A renal biopsy showed an acute interstitial nephritis but no changes suggestive of the haemolytic uraemic syndrome. He recovered normal renal function after treatment with haemodialysis and prednisone 20 mg daily for five days. Previous assumptions about the renal lesion in patients with malignancy-associated microangiopathic haemolytic anaemia may need review.