['Diabetes mellitus (DM) is closely associated with hepatocarcinogenesis. This study explores the prognostic impact of DM in patients who received curative therapy for localized hepatocellular carcinoma (HCC).', 'Patients who had been diagnosed with stage I or II HCC in 2003 and 2004 and received surgical resection or local ablation therapy were identified from the population-based Taiwan National Cancer Registry. Data pertaining to DM and other comorbidities were retrieved from the Taiwan National Health Insurance database. Liver cancer-specific survival (LCS), liver disease-related survival (LDS) and overall survival (OS) rates were compared between patients with and without DM. The presence of other comorbidities and tumor status were adjusted using multivariate analysis.', 'A total of 931 patients who fulfilled the study criteria were analyzed; 185 (20%) of them had DM (type 1 or type 2). The LCS, LDS, and OS rates were significantly worse for patients with DM than patients without DM (all p < .001). After adjusting for age, sex, tumor stage, treatment, and the presence of other comorbidities, DM remained an independent predictor of poorer LCS (hazard ratio [HR] = 1.57; p < .001), LDS (HR = 1.70; p < .001), and OS (HR = 1.69; p < .001). The associations between DM and mortality were consistent among subgroups, irrespective of tumor size, stage, treatment modality, and liver cirrhosis.'] Is diabetes mellitus associated with increased mortality in patients receiving curative therapy for hepatocellular carcinoma?