Objective: The impact of DM on post-operative morbidity and mortality after valve surgery is less well defined and the results of the studies are controversial. This study evaluated the effects of DM on post-operative short-term morbidity after isolated mitral valve replacement. Methods: The study population included 214 consecutive patients undergoing isolated mitral valve replacement (MVR) with mechanical valves under cardiopulmonary bypass (CPB). Patients were divided into two groups; diabetics (group I, n=36) and non-diabetics (group II, n=178). The groups were compared with respect to pre-and postoperative creatinine and blood urea nitrogen (BUN) levels, post-operative cerebrovascular disorders, arrhythmia, post-operative revision due to blood loss, surgical site infection, post-opertive extubation time, intensive care unit (ICU) and in-hospital stay time, CPB and aortic cross-clamp time. Results: In the diabetic group, post-operative rate of cerebrovascular disorders (13.9% vs. 2.8%; p=0.015), intubation time (11.5±7.6 h vs. 10.4±15.9 h; p=0.001), length of ICU stay (3.5±2.9 d vs. 2.7±2.1 d; p=0.001) and in-hospital stay (14.4±8.9 d vs. 11.1±6.9 d; p=0.023), rate of surgical site infection (19.4% vs. 3.9%; p=0.003), revision requirement rate (16.7% vs. 6.2%; p=0.045) were significantly higher. DM was also identified as an independent risk factor for surgical site infection, cerebrovascular disorder, arrhythmia and requirement of revision. Conclusion: This study showed that DM not only increases short-term morbidity due to its multiple effects but is also an independent risk factor for surgical site infection, cerebrovascular disorder, arrhythmia and requirement of revision after isolated mitral valve replacement procedures.