Diabetes mellitus (DM) and hyperglycemia are known predictors of adverse outcome in different tumor entities. The present study investigated the effect of DM and pre-surgery blood glucose levels on cancer specific survival (CSS), overall survival (OS), and disease-free survival (DFS) in non-metastatic soft tissue sarcoma (STS) patients. A total of 475 STS patients who underwent curative resection were included in this retrospective study. CSS, DFS, and OS were assessed using Kaplan-Meier curves. The association between pre-existing DM as well as mean pre-surgery blood glucose levels and all 3 survival endpoints was analyzed using Cox-hazard proportional (for OS and DFS) and competing risk regression models (for CSS). In unadjusted analysis, DM was significantly associated with adverse CSS (sub-hazard ratio [SHR]: 2.14, 95% confidence interval [CI] 1.18-3.90, p = 0.013) and OS (hazard ratio [HR]: 2.05, 95% CI 1.28-3.28) and remained significant after adjusting for established prognostic factors (CSS: adjusted SHR 2.33, 95% CI 1.21-4.49, p = 0.012; OS: adjusted HR 1.96, 95% CI 1.17-3.28, p = 0.010), respectively. There was no significant association of DM with DFS (p = 0.149). The mean pre-surgery glucose levels were not significantly associated with inferior outcome (CSS: p = 0.510, OS: p = 0.382 and DFS: p = 0.786). This study shows, that DM represents a negative prognostic factor for clinical outcome in STS patients after curative resection.