24 children with symptomatic urinary tract infection (UTI) underwent systematically ultrasound studies (US) and 99mTc-DMSA renal scans. Among the 15 patients considered as acute pyelonephritis (APN) on clinical grounds, the scan was abnormal in 12 cases, in contrast with only 1 abnormal scan in the clinical subgroup of the lower UTI. Among the 10 abnormal scans that were repeated later on, 6 did completely normalize. US showed only once a parenchymal appearance suggestive for APN. Our findings suggest that the DMSA scan has to be considered at present as the most sensitive imaging technique for the detection of APN.