PURPOSE: The purpose of the study was to compare CT with scintigraphy in the detection of parenchymal lesionsof acute pyelonephritis in children, and to assess the diagnostic value of CT. MATERIALS AND METHODS: This studyinvolved 32 children with acute pyelonephritis ; their ages ranged from 1 month to 10 years. Renal CT , TC-99mDMSA planar and SPECT images, and medical records were retrospectively reviewed. We evaluated the number, size,shape, density, and location of pyelonephritic lesions, as seen on CT and scintigraphic images. RESULTS: In 43involved kidneys, 193 parenchymal lesions of acute pyelonephritis were identified. The results of CT were abnormalin 42 kidneys (98%), and those of scintigraphy, in 39(91%). CT showed single or multiple hypoenhancing parenchymallesions ; these were streaky(n=151), wedge-shaped (n=34), or oval (n=8), and ranged from about 3-30mm in maximumdiameter. Abscess (n=5), renal fascial thickening (n=6) and thickening of the bridging septae (n=7) wereassociated. Scintigraphic findings were diffuse or localized area of varying degrees of diminished corticalactivity, and these were more precisely identified on SPECT than on planar images. For the detection of 55 of 193pyelonephritic lesions, CT was more sensitive than scintigraphy ; 29 of the 55 lesions were less than 5 mm indiameter. CONCLUSION: For the detection of pyelonephritic lesions, particularly smaller ones, and for theevaluation of complications such as abscess formation, CT is more sensitive than Tc-99m DMSA scintigraphy. Weconclude that in children with subtle scintigraphic findings who are in serious clinical condition or in whomcomplications are suspected, CT is a useful tool for assessing a therapeautic plan and the prognosis of acutepyelonephritis.