Urinary tract infection is common in children. The available gold standard methods for diagnosis, Tc-99m dimercaptosuccinic acid (DMSA) scan and computed tomography (CT) are invasive and expensive. This study was performed to assess the role of power Doppler ultrasound (PDU) for diagnosis of acute pyelonephritis (APN) compared with Tc-99m DMSA scan. A prospective study was conducted in 34 children with the mean age of 2.8+/-2.7 years who were hospitalized with the first episode of febrile urinary tract infection. All children were examined in the first 3 days of admission by PDU and Tc-99m DMSA scan. Patients with congenital structural anomaly were excluded. Each kidney was divided into three zones. The comparison between PDU and DMSA scan was performed on the basis of patients and renal units. According to the patient's number, sensitivity, specificity, positive and negative predictive values, and accuracy of PDU were 89%, 53%, 70%, 80%, and 74%, respectively, but based on the renal units, changed to 66%, 81%, 46%, 91%, and 79%, respectively. Although PDU has the potential for identifying APN in children, it is still soon to replace DMSA scan.