The diagnosis of membranoproliferative glomerulonephritis is made by its distinctive glomerular morphology. Early there may be an acute glomerulonephritis and late, a lobular glomerulonephritis. Hypocomplementemia often accompanies the disease in children. Onset is usually in childhood as a nephrotic or acute nephritic syndrome or a chance proteinuria. Origin is unknown and onset may be insidious. The disease is typically long standing with, terminally, rapid deterioration. Children may have a long interval of ‘silent’ nephritis. Activation of C3 by an alternate pathway involving a nephritic factor and the C3 proactivator produces the hypocomplementemia but has not been demonstrated to produce the nephritis. No treatment is consistently successful. The disease can recur in a renal transplant.