Renal sonography detects abnormality in only 40% of pediatric pyelonephritis. In eight patients shown to have acute pyelonephritis by 99mTc DMSA renal cortical scintigraphy, five were found to have focal abnormalities of renal perfusion by color Doppler sonography in the same sites as the scintigraphic defects (sensitivity-63%). Two of the five patients had normal plain sonograms. False positive studies occurred in patients with documented chronic renal scarring. The specificity of vascular asymmetry was 70%. This preliminary report suggests that, particularly in the patient without pre-existing renal scarring, color Doppler evaluation of the renal vasculature may increase the sensitivity of sonography in the diagnosis of pyelonephritis in children.