PURPOSE: To evaluate postcontrast CT findings of acute pyelonephritis and correlate these with clinical findings and severities. MATERIALS AND METHODS: We retrospectively reviewed the medical records and CT scans of 50 patients with abnormal CT findings among 52 patients of acute pyelonephritis whose postcontrast CT scans had been examined. Fifty cases of acute pyelonephritis were classified into three subgroups on the basis of postcontrast CT findings : Group I (n=20, 40%) wedge-shaped lesions; Group II (n=13, 26%) mass-like lesions; Group III (n=17, 34%) renal abscess formation. In each group, clinical findings and severity were analyzed and correlated with CT findings. The results were statistically analyzed. RESULTS: Although mean values of clinical parameters of group I were lower than those of group II and III with regard to all clinical parameters (including maximal temperature and duration of fever, flank pain, leukocytosis, and admission period), there was no statistically significant correlation among the three groups (p>0.05). All cases were successfully treated with antibiotics only, despite the high rate of abscess formation (34%). CONCLUSION: Acute pyelonephritis spans a continuum of CT findings of varying severity from wedge-shaped or mass-like lesions to multifocal abscesses ; postenhanced CT scan shows high sensitivity (96%) in the detection of acute pyelonephritis. Although the clinical course of groups of mass-like lesions and abscess formation was longer and more severe than that of wedge-shaped lesions, there was no statistically significant clinicoradiologic correlation among the three groups.