We carried out a retrospective investigation in 220 patients to assess the influence of various parameters on the long-term course of membranoproliferative glomerulonephritis (MPGN) type I. 50 patients (23%) died during the follow-up period of 59 months on average, in another 57 (26%) end-stage renal failure developed. 54 patients (24%) suffered from chronic renal failure, stable renal function (creatinine below 1.3 mg/dl) was preserved in 59 patients (27%). 5 years after biopsy 49% of the patients had already died or needed regular dialysis treatment; after 10 years this proportion increased to 64%. Morphological findings: The outcome was--with the exception of focal crescent formations--not determined by the severity of glomerular changes; the survival rate, however, decreased significantly, if tubulointerstitial lesions were present as defined by acute renal failure, interstitial fibrosis or a combination of both. Clinical parameters: A progressive deterioration of renal function and an increasing number of renal deaths was noticed, when elevated serum creatinine levels at the time of biopsy and high blood pressure values during the follow-up period were observed. 26 patients died from hypertension, 18 of whom before reaching end-stage renal failure. Nephrotic syndrome and the degree of proteinuria as well as antiphlogistic and immunosuppressive treatment did not influence the prognosis of MPGN type I.