The current data suggest that the usual laboratory and clinical information used to diagnose acute pyelonephritis cannot reliably identify most patients with renal parenchymal inflammation. Acute pyelonephritis occurs frequently in the absence of vesicoureteral reflux. 99Tc cortical scintigraphy is the preferred imaging technique for establishing the diagnosis of acute pyelonephritis and should be used routinely in every child with suspected pyelonephritis. A new imaging protocol based upon renal scintigraphy and dimercaptosuccinic acid scanning is presented. Excretory renography and computerized tomography have only a very limited role in the evaluation of a child with pyelonephritis.