Patient survival and renal outcome were followed in 25 patients with biopsy confirmed Wegener's granulomatosis and renal involvement. Fourteen out of 25 patients required dialysis on admission, 11/25 patients did not. All patients were treated with a novel protocol comprising methylprednisolone and cyclophosphamide. The median follow-up observation was 36 months (12-113 months). With the exception of 1 patient (who died from causes not related to Wegener's granulomatosis) all patients are alive. Among the patients initially requiring dialysis (n = 14) 4 are in terminal renal failure after 0, 7, 21 and 38 months respectively. In the nondialysis group (n = 11) only 1 patient subsequently required chronic dialysis 30 months after clinical admission. Renal failure was due to non-compliance with immunosuppressive therapy in at least 2 patients. Percentage of obsolescent glomeruli and the degree of tubulointerstitial lesions, but not active glomerular lesions (crescents, necroses) predicted renal outcome. The major cause of renal functional impairment was relapse of Wegener's granulomatosis usually within 2 years after clinical remission. Therefore prolonged treatment with cyclophosphamide for at least 2 years after clinical remission is recommended. Two patients with initially negative immunohistology had a second renal biopsy which revealed de novo appearance of mesangial IgA deposits.