We report a patient who presented with malignant hypertension and renal failure. He was treated with lisinopril, spironolactone, and nifedipine retard for blood pressure control. Subsequent renal function showed further deterioration, but it then improved after withdrawal of the angiotensin converting enzyme inhibitor (ACE I). The diagnosis of classical polyarteritis nodosa was established with aneurysmal dilatation demonstrable in the renal vasculature. His renal impairment improved further following immunosuppressive therapy and the disease has remained inactive 4 years after first presentation. This is the first reported case of acute renal failure associated with the use of ACE I in polyarteritis nodosa.