['Conflicting data exist on the interaction of diabetes mellitus with outcomes in patients with renal cell carcinoma. We evaluated the association of diabetes mellitus with survival in patients with clear cell renal cell carcinoma treated with nephrectomy.', 'We reviewed the records of 1,964 patients treated surgically for sporadic, unilateral, M0 clear cell renal cell carcinoma between 1990 and 2008. One pathologist re-reviewed all specimens to confirm clear cell renal cell carcinoma. We matched 257 patients with diabetes 1:2 to referent patients without diabetes according to clinicopathological and surgical features. Cancer specific and overall survival was estimated using the Kaplan-Meier method. Cox models were used to evaluate associations with outcomes.', 'A total of 257 patients (13%) had diabetes mellitus. They were significantly older and more likely to be obese, and had higher Charlson scores, renal impairment and smoking rates, and worse performance status at surgery (p\xa0<0.001). Pathological features were similar between the groups. Median postoperative followup was 8.7 years. Five-year cancer specific survival was similar in patients with and without diabetes (82% vs 86%, p = 0.1) while 5-year overall survival was significantly worse in those with diabetes (65% vs 74%, p\xa0<0.001). On multivariable analysis diabetes mellitus independently predicted cancer specific mortality (HR 1.55, 95% CI 1.08-2.21, p = 0.02) and all-cause mortality (HR 1.32, 95% CI 1.06-1.64, p = 0.01).'] Is diabetes mellitus independently associated with an increased risk of mortality in patients with clear cell renal cell carcinoma?