Objective: To determine whether diabetes mellitus (DM) effects progression-free survival (PFS) and overall survival (OS) in women with epithelial ovarian cancer (EOC). Materials and Methods: Tongji Hospital (Wuhan, China) patients presenting with EOC between 2004 and 2012 were included in a retrospective cohort study. Patients were monitored for PFS and OS through October 2014. Kaplan-Meier and log rank statistical methods were used to compare PFS and OS between diabetes mellitus patients and non-diabetic (ND) patients. Results: A total of 257 patients were included in the study and 64 (24.9%) were diagnosed with diabetes mellitus. Non-diabetic and diabetic mellitus patients were evenly distributed in age, malignant family history, tumor stage, pathology grade, body mass index (BMI), and protein levels of CA125. These results demonstrated that the DM group had worse PFS (31.0 vs. 44.0 months, p = 0.008) and OS (34.0 vs. 55.0 months, p = 0.002) when compared to the ND group. Conclusion: EOC patients with diabetes mellitus have reduced PFS and OS than patients without diabetes.