The results of cross-sectional studies addressing early preintrusive atherosclerosis in type I diabetic patients are conflicting. In an observational longitudinal study we determined the course of carotid artery intima-media thickness (IMT) over a period of 2.5 years in mean. A total of 102 patients with type I diabetes mellitus (age : 40 years, diabetes duration greater than or equal to2 years at baseline examination) who were participants of the baseline examination was studied again in a follow-up. HbA1c, albumin excretion rate (AER), lipids, systolic and diastolic blood pressure, retinopathy, and current smoking status were assessed at baseline and followup. The IMT of the common carotid artery was measured by highresolution ultrasound, the maximum IMT was evaluated. The annual progression rate (APR) was calculated from the difference between baseline and follow-up IMT reading and the time between both examinations. The follow-up IMT was significantly higher, compared to the baseline measurement: 0.65 +/- 0.18 vs. 0.57 +/- 0.14 mm (p < 0.001), the mean APR was 0.033 mm/year. The APR was correlated with age (r = 0.337, p < 0.01), diabetes duration (r = 0.252, p < 0.05), hypertension (r = 0.225, p 0.05), and systolic blood pressure (r = 0.281, p < 0.05) at the baseline examination. Comparing subgroups, defined according to APR tertiles, with no IMT progression (First fertile, mean APR - 0.012 mm/year), mild progression (second tertile, mean APR 0.037 mm/year), and advanced progression (third tertile, mean APR 0.088 mm/year), patients with advanced progression significantly (p < 0.05) more often had hypertension and nephropathy than subjects with mild progression. In a multiple linear regression analysis, the changes of plaque frequency and of the nephropathy status between baseline and follow-up examinations were independent predictors of the APR.