Background/aims: Diabetic retinopathy is an important complication of diabetes mellitus. It is supposed that the coexistent high blood glucose and sialic acid in diabetes mellitus play an important role. In this study, we investigated serum total sialic acid levels related to glysemic control, blood pressure, retinopathy and serum lipid levels in diabetic patients. Methods: We selected 62 patients with type 2 diabetes mellitus as a research group of those 31 patients did not have any retinopathy, in the remaining 20 patients had background retinopathy, 11 patients had background retinopathy and maculopathy. As a control group we selected 31 normal (healthy) subjects at random and matched them for age and sex with patients. Results: Serum total sialic acid levels in the patients were found significantly higher than normal subjects (p<0.001). Serum sialic acid levels were especially elevated in patients with diabetic retinopathy when compared to the group without retinopathy (p<0.01). In the patients with retinopathy, we found correlation between total serum sialic acid levels, erythrocyte sedimentation rate, systolic and diastolic blood pressures. In the patients without retinopathy, we found high correlation between total serum sialic acid levels, erythrocyte sedimentation rate, systolic blood pressures and fructozamine levels. Conclusions: As a conclusion, gradually increasing sialic acid levels in diabetic patients by destroying the cell structure plays an important role in development of retinopathy. There is a relationship of sialic acid with high blood pressure that has an influence in retinopathy formation. It is possible to prevent excessive increasing of serum sialic acid levels by a good diabetic regulation and keeping blood pressure in normal ranges, thus development of this complication retinopathy can be decreased.