Abstract Objective Diabetes mellitus (DM) is a risk factor for endometrial cancer and is associated with poorer outcomes in breast and colon cancers. This association is less clear in epithelial ovarian cancer (EOC). We sought to examine the effect of DM on progression-free (PFS) and overall survival (OS) in women with EOC. Methods A retrospective cohort study of EOC patients diagnosed between 2004 and 2009 at a single institution was performed. Demographic, pathologic and DM diagnosis data were abstracted. Pearson chi-square test and t test were used to compare variables. The Kaplan–Meier method and the log rank test were used to compare PFS and OS between non-diabetic (ND) and DM patients. Results 62 (17%) of 367 patients had a diagnosis of DM. No differences in age, histology, debulking status, or administration of intraperitoneal chemotherapy between ND and DM patients were present, although there were more stage I and IV patients in the ND group (p=0.04). BMI was significantly different between the two groups (ND vs. DM, 27.5 vs. 30.7kg/m2, p<0.001). While there were no differences in survival based on BMI, diabetic patients had a poorer PFS (10.3 vs. 16.3months, p=0.024) and OS (26.1 vs. 42.2months, p=0.005) compared to ND patients. Metformin use among diabetic patients did not appear to affect PFS or OS. Conclusions EOC patients with DM have poorer survival than patients without diabetes; this association is independent of obesity. Metformin use did not affect outcomes. The pathophysiology of this observation requires more inquiry.