Objective: To compare corneal endothelial cell morphology, density and central corneal thickness in type 2 diabetic and non-diabetic healthy volunteers. Material and Methods: This prospective clinical study included 30 patients (60 eyes) with type 2 diabetes, and 51 (102 eyes) non-diabetic healthy volunteers. Body mass indexes of the diabetic patients were calculated. Fasting blood glucose (FBG) and HbA1c levels were also measured. The controls had no diabetes confirmed by two FBG measurements below 100 mg/dL. The endothelial cell density (ECD), average cell size (ACS), standard deviation (SD), coefficient of variation of cell area (CV), the percentage of hexagonal cells (HC), and the central corneal thickness (CCT) were recorded with the specular microscope. Results: The mean age of the type 2 diabetic group and the healthy controls were 54.8±9.6 and 53.3±8.2 years, respectively. Two groups were similar in terms of age and gender (p=0.454, p=0.672, respectively). Type 2 diabetic subjects did not differ statistically from the non-diabetic healthy volunteers concerning ECD, ACS, SD, CV, HC, and CCT (p=0.815, p=1.000, p=0.868, p=0.934, p=0.087, p=0.236, respectively). A positive correlation was detected between HbA1c and CCT in the diabetic patients (r=0.297, p=0.026). CCT showed a tendency to increase in the ones who were diabetics more than a decade when compared to the ones who had the disease less than a decade (537.2±32.0 μm, 519.0±28.2 μm, respectively). However, this difference was not statistically significant (p=0.06). Conclusion: Structural changes in corneal endothelial cells secondary to long-term and uncontrolled diabetes mellitus may result in increased corneal thickness. While screening diabetic patients for complications of diabetes mellitus, effects of chronic hyperglycemia on cornea should also be taken into consideration. © 2014 by Türkiye Klinikleri.