Background: As the prevalence of type 2 diabetes mellitus rises, so do its attendant, micro vascular complications. Besides, diabetic retinopathy, patients with diabetes are prone to developing corneal endothelial damage, keratoepitheliopathy in the form of recurrent corneal erosions, persistent epithelial defects, and superficial keratitis. Objectives: To find out the correlation between Diabetes mellitus and Central corneal thickness (CCT). Material and Methods: It was a hospital based, Case–Control study. A total of 100 patients, 40–70yrs of age, participated in the study, of whom 50 were diabetic and 50 were non–diabetic. Consenting patients of age 40–70yrs was done, attending Ophthalmology OPD of medical college in Lucknow, who did not have any corneal pathology were divided into two groups – diabetic and non–diabetic. After thorough local and systemic examination, the central corneal thickness was measured using Ultrasound pachymetry. Results: Mean CCT was thicker in diabetic group (575.53μm) when compared to non–diabetic group (560.40μm). The difference between the 2 groups was significant (p<0.001). Mean CCT in diabetic patients was 575.53±7.8μm. Mean duration of diabetes was 9.53±1.9 yrs. The correlation between CCT and duration of diabetes was not significant (p=0.158). Conclusion: The CCT in diabetic patients was thicker compared to CCT in non–diabetics. Therefore, diabetes can increase the CCT but there is no significant correlation between duration of diabetes and CCT.