Aims/hypothesis. Hyperglycaemia predicts microvascular complications but data on macrovascular disease are limited. We searched for predictors of carotid artery intima-media thickness in young adults with Type I (insulin-dependent) diabetes mellitus. Methods. A total of 71 children (F/M = 34/37) were followed after their diagnosis until they reached 32 ± 1 years of age, when duration of diabetes averaged 22 ± 1 years. Cardiovascular risk markers [lipids, blood pressure, smoking, urinary albumin excretion rate, lifetime glycaemic exposure (A 1c months), exercise habits, alcohol consumption, family history] were evaluated at age 21 ± 1 for the baseline examination and at age 32 ± 1 years for the follow-up examination years. During follow-up, intima-media thickness of common and internal carotid arteries and the carotid bulb were quantitated using a high-resolution B-mode ultrasound.Results. In univariate analysis, age, BMI, blood pressure, lifetime glycaemic exposure, a positive family history of Type II (non-insulin-dependent) diabetes mellitus, hypertension and cardiovascular disease were predictors of carotid intima-media thickness. In multivariate analysis, a positive family history of Type II diabetes predicted maximal (p < 0.05) and common (p < 0.005) carotid artery intima-media thickness, family history of hypertension predicted increases in maximal (p < 0.04), and far wall (p < 0.006) carotid artery intima-media thickness, and lifetime glycaemic exposure was an independent predictor of increased carotid bulb thickness (p < 0.03). Conclusion/interpretation. Positive family histories of Type II diabetes and hypertension are independent predictors of carotid intima-media thickness in patients with Type I diabetes, and could therefore predispose these patients to atherosclerosis [Diabetologia (2002) 45:711-718]