Although early diagnosis of urinary tract infection is important, the radiologic evaluation is still controversial because of the low sensitivity and the lack of cost-effectiveness. This study was carried out to evaluate the clinical utility of high resolution triple head Tc-99m-DMSA SPECT imaging in urinary tract infection. We prospectively performed Tc-99m-DMSA planar and SPECT imaging, ultrasound of kidney (US), intravenous pyelography (IVP) and voiding cystourethrography (VCU) in all 60 adult patients with UTI [26 with first episode of acute pyelonephritis (APN), 22 with recurrent APN, and 12 persistent asymptomatic pyuria] and 25 normal persons. To assess reversibility of the renal cortical defect (RCD), Tc- 99m-DMSA SPECT was repeated 1 to 8 months later in those patients with abnormal initial findings. Overall detection rate of Tc-99m-DMSA SPECT imaging was 83% (50/60), but planar, US, IVP and VCU showed abnormal findings in 68%, 28%, 32% and 13%, respectively. 25 out of 27 patients with nonnal or single RCD were all normal in other radioligic studies. Only two patients showed vesicoureteral reflux (VUR) on VCU (grade I) and mild hydronephrosis on IVP. But, high proportion of those with multiple RCD showed abnormal findings on US (17/33), IVP (18/33), and VCU (7/33): 67% in any of these 3 studies. Especially, 3 out 7 patients with VUR showed multiple RCD on Tc-99m- DMSA SPECT without any abnormality on IVP or US. 25 normal persons showed normal findings in all studies except one false positive finding on Tc-99m-DMSA SPECT imaging. Follow- up Tc-99m-DMSA SPECT was done in 28 patients (13 with single RCD, 15 with multiple RCD). All 13 patients with single RCD showed improvement. Those with multiple RCD presented improvement in 4, no change in 10, and aggravation in 1 on follow-up studies. With these results, we conclude: 1) Tc-99m-DMSA SPECT imaging is superior to planar imaging, US, IVP or VCU in detection of renal lesion in urinary tract infection. Tc-99m-DMSA SPECT is useful as a initial diagnostic tool in adult patients with urinary tract infection. 2) The multiple RCD on Tc-99m- DMSA SPECT represent the high probability of irreversible tissue change and need of extensive urological work-up.