PURPOSE: Renal scar or reflux nephropathy, known as a major cause of end-stage renal failure and hypertension in children and young adults, is frequently detected in pediatric urinary tract infection(UTI) patients at their first infections. So early and accurate diagnosis, and follow up of renal scar are very important. We performed this study to recognize the importance of radiologic examinations for detection of renal scar and vesicoureteral reflux(VUR) in pediatric UTI patients at their first attacks, and to compare the accuracy and usefulness of DMSA renal scan with renal ultrasonography and IVP in early detection and follow up of renal scar. We also wanted to find the association of renal scar with VUR detected by VCUG, and increased C-reactive protein(CRP) level. METHODS: We studied on 41 pediatric UTI patients without past medical history of UTI, who were admitted to the Department of Pediatics, Kangbuk Samsung Hospital from May 1993 to August 1995. On admission a blood sample was taken for the determination of CRP. Renal ultrasonography and DMSA renal scan were performed within five days after admission. Eight weeks later, with repeated studies of renal ultrasonography and DMSA renal scan, IVP and VCUG were also performed for all patients. RESULTS: 1) The incidence of UTI was most prevalent in infancy grou(56%). The ratio of male to female patients was 4.8:1 under the age of one year, and 1:2 over the age of one year. 2) At admission, 21 of 41 patients(51%) showed renal scars in the DMSA renal scans. At follow up of DMSA renal scans, 8 weaks later, 7 of 21 initially abnormal cases(33%) became normal while 14 cases(67%) continued to show renal scars. Twenty initially normal cases continued to show normal DMSA renal scans at follow up. 3) Renal ultrasonography showed 10 abnormal cases among 41 cases(24%) at admission, and 7 abnormal cases(17%) at follow up. IVP showed 13 abnormal cases among 41 cases(32%). 4) For detection of renal scar, sensitivity and specificity of DMSA renal scan were 95% and 100%, sensitivity and specificity of renal ultrasonography were 45% and 90%, and sensitivity and specificity of IVP were 59% and 100% retrospectively. 5) VCUG showed reflux in 13 patients among 41 patients(32%). Among 20 patients with normal DMSA renal scan, only two patients(10%) showed VUR in VCUG, and they were classified as grade I and II VUR by International Reflux Study Committee classifications. Among 21 patients with abnormal by DMSA renal scan, 11 patients(52%) showed VUR in VCUG, of whom 9 patients were classified as severe reflux above grade III. 6) The mean CRP level in the patients with normal DMSA renal scan was 9.6mg/L, significantly lower than mean CRP level of patients with abnormal DMSA renal scan which was 60.57mg/L(p<0.01). CONCLUSIONS: For early detection of renal scars and reflux nephropathy, appropriate radiologic investigations including DMSA renal scan and VCUG should be done to all pediatric UTI patients at their first attacks. DMSA renal scan seemed to be better radiologic method than renal ultrasonography and IVP in early detection of renal scar and have association with VUR. We also found that blood CRP level is easy and useful test for early suspection of upper UTI.