Glomerulonephritis (GN) is the leading cause of chronic kidney disease among recipients of renal transplants. Because modern immunosuppressive regimens have reduced the incidence of rejection-related graft loss, the probability and clinical significance of posttransplantation GN (PTGN) requires reevaluation. In this Canadian epidemiologic study, we monitored 2026 sequential renal transplant recipients whose original renal disease resulted from biopsy-proven GN (36%), from presumed GN (7.8%), or from disorders other than GN (56%) for 15 yr without loss to follow-up. Kaplan-Meier estimates of PTGN in the whole population were 5.5% at 5 yr, 10.1% at 10 yr, and 15.7% at 15 yr. PTGN was diagnosed in 24.3% of patients whose original renal disease resulted from biopsy-proven GN, compared with 11.8% of those with presumed GN and 10.5% of those with disorders other than GN. Biopsy-proven GN in the native kidney, male gender, younger age, and nonwhite ethnicity predicted PTGN. Current immunosuppressive regimens did not associate with a reduced frequency of PTGN. Patients who developed PTGN had significantly reduced graft survival (10.2 versus 69.7%; P < 0.0001). In summary, in the Canadian population, PTGN is a common and serious complication that causes accelerated graft failure, despite the use of modern immunosuppressive regimens.