Malignancies are one of the main causes of mortality in diabetic patients; however, to date, very limited data have been reported on the specific influence of type 2 diabetes mellitus (T2DM) on the survival of patients with renal cell carcinoma (RCC). In the present long-term retrospective study, we investigated whether T2DM may influence the overall survival (OS), cancer-specific survival (CSS), and progression-free survival (PFS) in patients with surgically treated RCC. Medical records of 924 patients treated by radical or partial nephrectomy for sporadic, unilateral RCC were reviewed. Patients with type-1 DM and with T2 DM receiving insulin treatment were excluded. Survival estimates were calculated according to the Kaplan-Meier method and compared with the log-rank test. Univariate and multivariate analyses were performed using the Cox regression model.Of the 924 RCC patients, 152 (16.5%) had T2DM. Mean follow-up was 68.5 months. Mean OS was 41.3 and 96.3 months in T2DM and non-T2DM patients, respectively (P < 0.0001).The estimated CSS rates at 1, 3, and 5 years in T2DM versus non-T2DM patients were 63.4% versus 76.7%, 30.4% versus 56.6%, and 16.3% versus 48.6%, respectively (P = 0.001). Mean PFS was significantly lower (31.5 vs 96.3 months; P < 0.0001) in the T2DM group. At multivariate analysis, T2DM was an independent adverse prognostic factor for OS (hazard ratio [HR] = 3.44; 95% confidence interval [CI]:2.40-4.92), CSS (HR = 6.39; 95% CI: 3.78-10.79), and PFS (HR = 4.71; 95% CI: 3.11-7.15). In conclusion, our findings suggest that patients with RCC and pre-existing T2DM have a shorter OS, increased risk of recurrence, and higher risk for kidney cancer mortality than those without diabetes.