Two patients with previously undescribed renal manifestations of Wegener's granulomatosis are described. A 24 year old man, who presented with typical necrotizing granulomatous sinus disease and cavitary pulmonary lesions, had multiple bilateral renal arterial aneurysms demonstrated angiographically. One of these aneurysms ruptured, leading to a massive perinephric hematoma. The bleeding artery was successfully occluded with Gelfoam embolization, thereby obviating the need for nephrectomy. A 60 year old woman presented with glomerulonephritis and mononeuritis multiplex two years before the development of classic necrotizing granulomatous inflammation of her sinuses and nose, along with pulmonary nodules. In addition, her left ureter became obstructed due to necrotizing vasculitis of the periureteral vessels. Both patients responded dramatically to cyclophosphamide therapy. The diagnosis of Wegener's granulomatosis should be considered in patients who present with multiple renal aneurysms, a spontaneous perinephric hematoma, necrotizing glomerulitis or ureteral obstruction due to vasculitis, even though the characteristic granulomatous respiratory involvement may be absent at that time. It is important to recognize these unusual renal manifestations as features of Wegener's granulomatosis because of the therapeutic efficacy of cytotoxic immunosuppressive agents in this disease.