Seventy-six children with idiopathic MPGN have been followed at this medical center since 1957 (mean 10.6 years of disease). Seventy-one of the children have been treated with a regimen of prednisone (mean 7.7 years of treatment). Monotherapy with alternate-day prednisone was used in 50 of the children. Other immunosuppressive and cytotoxic drugs have not been used since 1981. In the 71 treated patients, the cumulative renal survival (creatinine less than 3.0 mg/dl (265.5 mumol/L)) was 82% in the tenth year and 56% in the twentieth year after disease onset. Cumulative renal survival, calculated from the date of initiation of the prednisone regimen, was 75% in the tenth year and 59% in the twentieth year. As our experience with this disease has increased, long-term cumulative renal survival has improved.