Accumulation of hyaluronan (HA) around smooth muscle cells in lesions of atherosclerosis in diabetic patients suggests that this protein plays an important role in diabetic angiopathy. The aim of this study was to determine the correlation between serum HA concentrations and diabetic angiopathy. Diabetic patients treated with or without an oral hypoglycemic agent and/or insulin for at least 1 year were recruited (n = 95). We also included 20 non-diabetic control subjects. We measured serum levels of HA, body mass index (BMI), fasting plasma glucose (FPG), HbA1c, total cholesterol, triglyceride, glycated albumin (GA), high sensitivity CRP (hs-CRP), monocyte chemoattractant protein (MCP)-1 and evaluated diabetes mellitus history, drug use and presence of related complications. Serum HA levels were significantly (P<0.05) higher in diabetic patients (83.6 ± 5.6 ng/ml, mean ± SEM) than in normal subjects (41.7 ± 12 ng/ml). In diabetic patients, serum HA concentration significantly correlated with FPG, HbA1c, GA, triglyceride and also significantly correlated with BMI, hs-CRP and MCP-1 and tended to be higher in diabetic patients with complications than in those without such complications. Our data suggest that serum HA level correlates with poor blood glucose control and diabetic angiopathy and that it could be used as a marker of diabetic angiopathy.