PURPOSE: The purpose of this study is to assess the ability of power Doppler sonography in the detection of acute pyelonephritis. MATERIALS AND METHODS: We performed gray scale sonography, power Doppler sonography, and Tc-99m DMSA scintigraphy of the kidney in 80 patients with symptoms suggesting upper urinary tract infection. All imaging studies were obtained within 4 days. On Tc-99m DMSA scintigraphy, decreased radioactivity or photopenic lesions were considered indicative of acute pyelonephritis. Triangular areas of decreased perfusion identified on power Doppler sonography were considered as parenchymal lesions of acute pyelonephritis. The results of gray scale sonography and power Doppler sonography were retrospectively analysed and compared with those of Tc-99m DMSA scintigraphy which was given as the standards of reference. RESULTS: For 40(85%) of the 47 patients with scintigraphy-proven acute pyelonephritis, power Doppler sonography diagnosed this condition on the correct side. The acute pyelonephritis which was not revealed by power Doppler sonography was observed in seven patients. Also, in three patients, false-positive indication of pyelonephritis was given by power Doppler sonography. Gray scale sonography showed positive findings in 23(49%) of 47 patients with positive findings on scintigraphy. CONCLUSION: Power Doppler sonography seems to be less sensitive than Tc-99m DMSA scintigraphy but significantly more sensitive than gray scale sonography for the detection of acute pyelonephritis in children. Power Doppler sonography shows promise as a noninvasive means of assessing renal cortical perfusion in children with clinically suspected acute pyelonephritis.