The results of cross-sectional studies addressing early preintrusive atherosclerosis in type 1 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 1 diabetes mellitus (age < or = 40 years, diabetes duration > or = 2 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 follow-up. The IMT of the common carotid artery was measured by high-resolution 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 tertile, 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.