In Japan, the school urinary screening system facilitates early detection and treatment of membranoproliferative glomerulonephritis (MPGN) in childhood. The present study investigated the long-term prognosis in 19 children with diffuse MPGN type I who received steroid therapy. Before signs of glomerulonephritis were confirmed, all patients displayed abnormal urinalysis results, predominantly through school urinary screening. Treatment comprised a regimen of alternate-day prednisolone after steroid pulse or cyclophosphamide therapy, and follow-up was continued for 10-24 years. Excluding 1 patient on short-term therapy, 18 patients received long-term alternate-day prednisolone therapy for 4-12 years. Treatment was discontinued when amelioration was confirmed on renal biopsy. As of the last observation, urinary abnormalities and hypocomplementemia had disappeared in 15 patients, while mild proteinuria without hypocomplementemia remained in 4 patients. No patients required hemodialysis. Moreover, no severe adverse effects attributable to treatment were identified other than mild short stature. Early detection and therapy using pulse methylprednisolone followed by alternate-day prednisolone was thus confirmed as safe and useful for treating diffuse MPGN type I.