Postinfectious glomerulonephritis (PIGN) is by far the most common cause of acute glomerulonephritis (AGN) in children. Numerous infectious agents, including bacteria, viruses, fungi, and parasites, have been implicated in PIGN. However, nephritogenic strains of group A betahemolytic streptococci are the most frequent culprits. Clinical manifestations of this syndrome, including hematuria, proteinuria, oliguria, fluid overload, and azotemia, are the result of proliferative and inflammatory changes of the renal glomeruli secondary to immunologic injury. In addition to PIGN, the differential diagnosis of a child who has AGN must include primary glomerular diseases such as membranoproliferative glomerulonephritis (MPGN), hereditary nephritis (Alport syndrome), and immunoglobulin (Ig)A nephropathy, as well as systemic diseases such as systemic lupus erythematosus, Henoch-Schönlein purpura, and hemolytic-uremic syndrome.