Sialic acid, an acetylated derivative of neuraminic acid, is reported to be a marker of micro- and macrovascular complications in diabetic subjects. The purpose of this study was to investigate the association of serum sialic acid and diabetic retinopathy. Serum sialic acid levels were measured in healthy non-diabetic control subjects, Type 2 diabetic patients without retinopathy (No DR), Type 2 diabetic patients with non-proliferative diabetic retinopathy (NPDR) and Type 2 diabetic patients with proliferative diabetic retinopathy (PDR). There was no significant difference in the serum sialic acid levels between the study groups (controls, 2.1 mmol/l; No DR, 2.5 mmol/l; NPDR, 2.2 mmol/l and PDR, 2.3 mmol/l). These results suggest that there is no association between serum sialic acid levels and diabetic retinopathy.