BACKGROUND Diabetics have abnormal corneal morphology along with higher rate of corneal endothelial cell loss and decreased corneal endothelial cell density and early onset of cataract. OBJECTIVE To evaluate the changes in corneal endothelium and corneal thickness in patients with diabetes mellitus after Manual Small Incision Cataract Surgery (MSICS) in eyes with brunescent Cataract. METHODS Sixty eyes of 60 patients with Type 2 diabetes mellitus and 60 eyes of 60 age matched healthy patients of advanced brunescent cataract underwent MSICS were evaluated. All the patients underwent specular microscopy for the corneal endothelial cell count of cornea and central corneal thickness pre-operatively, at one week, six weeks and 12 weeks post-operatively. The morphology, variation in the endothelial size and shape and percentage of hexagonal cells were assessed. RESULTS The mean pre-operative endothelial count in the control was higher than the diabetic group (p<0.001). The post-operative endothelial count loss in both the groups were statistically significant (one-way ANOVA p<0.001). On comparing post-operative endothelial loss in non diabetics (8.05%) to diabetic group, the diabetic group had significantly higher endothelial loss (14.19% p<0.001). There was also a significant increase in central corneal thickness in diabetics as compared to control (p = 0.004). The change in percentage hexagon cells in diabetic group was significantly higher than in non diabetic group (p = 0.005). Inter group change in coefficient of variance was not statistically significant (p=0.144). CONCLUSIONS Compared to non-diabetic patients, diabetic patients have more endothelial cells damage after MSICS. Corneal endothelial evaluation of diabetic patients is recommended before any intraocular surgery.