PURPOSE: The purpose of this study was to evaluate the CT findings of renal parenchyma infiltrated by pelvocalyceal transitional cell carcinoma. MATERIALS AND METHODS: This study included 28 patients in whom transitional cell carcinoma was dignosed after nephrectomy. CT findings were analyzed for the presence or absence of renal parenchymal infiltration; diagnostic criteria for this included parenchymal inhomogeneous low attenuation, ill-defined margin between the mass and renal parenchyma, or focal calyceal dilatation. To detect renal parenchymal infiltration by transitional cell carcinoma, we evaluated the frequency, sensitivity and specificity of each CT finding. RESULTS: Pathologic reports showed that renal parenchymal infiltration had occurred in 17 of 28 patients, (60.7%) ; on CT scans, renal parenchymal infiltration was seen in 15 of these 28 (53.6%). It two patients who did not show CT findings of renal parenchymal infiltration, pathologic examination revealed parenchymal invasion. All 15 patients who showed renal infiltration on CT had parenchymal inhomogeneous low attenuation (sensitivity: 88.2%, specificity : 100%), 13 showed ill-defined margin of the mass (sensitivity : 76.5%, specificity : 100%), and six showed focal dilatation of the calyx (sensitivity : 35.3%, specificity : 100%). CONCLUSION: In patients with pelvocalyceal transitional cell carcinoma, CT findings of parenchymal inhomogeneous low attenuation, ill-defined margin of mass, and focal calyceal dilatation suggest renal parenchymal infiltration, and these findings may be helpful in preoperative prognosis.