ABSTRACT
Renal cell carcinoma is a relatively rare tumor, accounting for approximately 3 percent of adult malignancies. Bilateral renal cell carcinoma, either synchronous or asynchronous, very rarely occurs and makes another urological dilemma. We experienced a case of unrecognized bilateral renal cell carcinoma ; which had been treated by radical nephrectomy after diagnosed as a left renal cell carcinoma, Robson stage IIIa, about 18 months later another mass was found in remaining kidney. Therefore, we performed wedge resection of the mass, and it was also diagnosed as a renal cell carcinoma. Reviewing of the initial abdomen-pelvis CF scan, mass in Rt. kidney had already been existed when left. renal cell carcinoma was diagnosed. This case was finally diagnosed with unrecognized bilateral synchronous renal cell carcinoma.