Objective: To investigate the relationship between serum interleukin-18 and interleukin-12 levels and clinicopathology of renal cell carcinoma. Methods: Peripheral blood samples were obtained from 20 healthy volunteers and 60 patients with renal cell carcinoma before curative surgery. IL-12 and IL-18 levels were determined by enzyme-linked immunosorbent assay. Results: Mean serum IL-12 and IL-18 levels were significantly higher in patients with renal cell carcinoma compared with healthy volunteers (P＜0.05) and mean serum IL-12 and IL-18 levels increased in patients as the pathologic stage progressed. A positive correlation was observed between serum IL-12 and IL-18 levels (P＜0.05). In patients with renal cell carcinoma, increasing serum IL-12 and IL-18 levels correlated with pathological stage and Fuhrman grade. Conclusion: Serum IL-12 and IL-18 might be useful tumor markers in patients with renal cell carcinoma.