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Obesity and diabetes are considered risk factors for Renal Cell Carcinoma (RCC). We aimed to explore whether insulin resistance (IR) plays an independent role in the development of RCC. In a hospital-based case-control study, we analyzed serum glucose, insulin, leptin and adiponectin levels among 60 incident RCC patients and 236 age- and gender-matched healthy controls. We assessed insulin resistance according to insulin levels, alone or controlled for diabetes mellitus (DM). An alternative measure of insulin resistance, such as the Homeostasis Model Assessment for Insulin Resistance (HOMA-IR) index, was also assessed with and without controlling for history of DM. We used logistic regression to estimate odds ratios (ORs) adjusted for possible confounders. The positive association of DM and waist to hip ratio as a measure of obesity with RCC was evident in the data set. Insulin levels controlled or not controlled for DM, however, were inversely associated with the risk for RCC; notably, an approximately 40% higher risk was observed in the 1sttertile when compared with the 2ndand 3rdtertile levels of insulin resistance. Similar results were obtained when HOMA-IR was alternatively used. The inverse associations persisted and were even strengthened after controlling for potential confounding factors in multivariate analyses. Our data suggest that insulin resistance may be inversely associated with RCC risk, independently of obesity, DM, lifestyle and hormonal confounding variables. Given the close interconnections among metabolic, inflammatory and immune pathways in RCC causation, it is difficult to infer which process actually initiates a pathologic cascade. The findings should be considered as preliminary data that need to be further confirmed in more appropriate study designs.