PURPOSE: To assess the value of computed tomography (CT) in the preoperative staging of transitional cellcarcinoma (TCC) of the renal pelvis. MATERIALS AND METHODS: We retrospectively evaluated the CT TNM staging of 38patients with TCC of the renal pelvis who had undergone preoperative abdominal CT examination between January 1990and January 1998. In CT staging for differentiation between early-stage (TO-2) and advanced-stage disease (T3-T4),three criteria were used, namely the presence or obliteration of the renal sinus fat layer, the smoothness orirregularity of margin between the tumor and renal parenchyma, and the presence or absence of hydronephrosisproximal to the tumor. CT staging was performed by two genitourinary radiologists blinded to the pathologicresults, and was compared with pathologic staging. RESULTS: Pathologic results revealed 19 cases of early stagedisease (TO=8, T1=9, T2=2) and 19 of advanced stage (T3=12, T4=7). Overall CT staging accuracy was 82%(31/38);fourcases were overstaged and three were understaged. In early-stage disease, sensitivity and specificity were 79%,and 84%, and in advanced stage disease were 83% and 80%. Three of four overstaged cases showed hydronephrosisproximal to the tumor. In the second CT staging, using proximal hydronephrosis of the tumor as a criterion forearly-stage disease, the sensitivity and specificity of early-stage disease were 95% and 75%, respectively, andthe specificity of advanced-stage disease was 95%. CONCLUSION: When hydronephrosis proximal to a tumor wasconsidered to be a sign of early stage disease, the CT staging of renal pelvic TCC was highly accurate.