Vascular markers of atherosclerotic burden allow atherosclerosis to be studied in the sub-clinical phase of the disease, and facilitate the assessment of new therapies for modifying coronary heart disease (CHD) risk factors. B-mode ultrasound enables non-invasive, direct visualization of the arterial wall. The intima media thickness of the carotid artery (CIMT) quantified using this technique, is a reliable marker of atherosclerotic burden. Furthermore, it demonstrates greater sensitivity in detecting early atherosclerosis compared with angiography. The validity of ultrasonographically-determined CIMT as a surrogate marker of atherosclerotic disease has been established; CIMT is positively associated with the incidence of coronary events, relates to atherosclerotic disease elsewhere in the arterial system and has common risk factors to the development of CHD. Furthermore, ultrasonographically-determined CIMT demonstrates good inter- and intra-observer reproducibility making it suitable for tracking the progression or regression of atherosclerotic disease over time. The validity of CIMT as a vascular marker of atherosclerosis progression has been demonstrated in clinical trials. Intervention studies have shown that modification of CHD risk factors can significantly reduce progression of CIMT. Hence, B-mode ultrasonography is being used increasingly to elucidate the efficacy of new therapies, enabling the benefits of treatment to be established more rapidly and with fewer patients compared with clinical outcome trials.