Over a 31-year period, we have encountered 13 children with a disease entity not reported by other clinics that leads to rapidly progressive crescentic glomerulonephritis. Gross hematuria, rapidly declining renal function, and a serum C3 level at the lower limit of normal or slightly depressed usually characterized the disease onset; hypertension and nephrotic syndrome were absent. Glomerular IgG was absent, but large C3-containing subepithelial deposits on the paramesangial basement membrane (GBM) were always present. Because of these deposits and because dense alteration of the GBM was found in 3 patients, the disease may resemble membranoproliferative glomerulonephritis type II, but is distinguishable on other morphological and clinical grounds. The absence of anti-neutrophil cytoplasmic antibody, tested for in 5 of 13 patients, is one of several ways the disease differs from the pauci-immune glomerulonephritis of adults. Clinically and by glomerular morphology, it also differs from severe poststreptococcal acute glomerulonephritis. Treatment with high-dose corticosteroids has been highly successful. Because in this series the disease occurred only in children under age 12 years and the amount of silver-positive mesangial matrix was normal, indicating absence of mesangial proliferation, it has been designated juvenile acute non-proliferative glomerulitis.