We investigated carotid intima-media thickness (IMT) and quantitative carotid stiffness (QCS) index in relation to plasma glycosylated hemoglobin A(1C) (HbA(1C)) and duration of diabetes mellitus in 337 Chinese diabetic patients. In categorical analyses, carotid IMT was 710 mum in subjects with a duration of diabetes mellitus < or = 2 years, 760 micorm in subjects with a duration of diabetes mellitus more than two years and with plasma HbA(1C) < 6.5% (P < 0.05), and 790 microm in subjects with a duration of diabetes mellitus more than two years but with plasma HbA(1C) > or = 6.5% (P < 0.01). The corresponding values for QCS values were 4.5, 4.6 and 5.1 (P < 0.05), respectively. In multiple stepwise regression analyses carotid IMT was significantly associated with the duration of diabetes mellitus, systolic blood pressure and serum concentration of total cholesterol, whereas QCS was significantly associated with age, HbA(1C), systolic and diastolic blood pressure (P < 0.05). In conclusion, carotid IMT as a structural measure of arterial wall is increased in patients with a longer history of diabetes mellitus, whereas QCS as functional index is mainly influenced by the quality of blood glucose control.