In order to examine the relationship between serum lipids and apolipoproteins and macrovascular disease in patients with Type 1 diabetes mellitus, 50 patients with Type 1 diabetes mellitus attending the diabetic clinics at St Mary's and St Charles' Hospitals, London were recruited into a cross-sectional study. B-mode ultrasound was used to measure intima-media thickness and define an arterial ultrasound score for each patient as a non-invasive indicator of atherosclerotic change. Intima-medial (i-m) thickness was significantly higher in those subjects with clinical evidence of macrovascular disease compared to those without macrovascular disease (0.865 +/- 0.191 vs 0.695 +/- 0.162 mm, p = 0.0038). In the study group there were significant correlations between i-m thickness and age (r = 0.65, p < 0.01), total serum cholesterol (r = 0.32, p < 0.01), and serum fibrinogen (r = 0.43, p < 0.01) but no other lipid or apolipoprotein variable. When i-m thickness was corrected for age there were significant correlations with total cholesterol (r = 0.43, p < 0.01) and LDL-cholesterol (r = 0.42, p < 0.01). Whereas total and LDL-cholesterol and serum fibrinogen concentrations were related to the extent of atherosclerotic disease by ultrasound techniques, there was no relationship with high density lipoprotein (HDL) or subfraction cholesterol concentrations. HDL-cholesterol may not be a useful marker for cardiovascular disease in Type 1 diabetes.