The simultaneous occurrence of renal cell carcinoma (RCC) and transitional cell carcinoma (TCC) in the same kidney is unusual. We report a 60-year-old man with ipsilateral synchronous renal adenocarcinoma and renal pelvic transitional cell carcinoma with severe hydronephrosis and a huge staghorn calculus in the ipsilateral kidney. The patient was admitted to the hospital because of right flank pain and hematuria which he had had for 4 months. X-ray and USG revealed a huge stone in the renal pelvis and hydronephrosis of the right kidney and IVP suggested a non-functional kidney. Right radical nephrectomy was done. A section of the specimen revealed a renal cell carcinoma located at the middleof right kidney and a papillary transitional cell carcinoma arising from the renal pelvis. This is a rare case of combined renal malignancies presenting in an atypical manner as hydronephrosis.