Arterial remodelling is a potentially important component in atherogenesis aimed at delaying the development of significant lumen compromise. Current knowledge on this phenomenon is mainly restricted to experimental evaluations and a few postmortem studies. We used high-resolution duplex ultrasound to study 5-year changes (1990 to 1995) in vessel geometry in a large random sample of the general population (Bruneck Study). Carotid arteries free of atherosclerosis and wall thickening preserved a normal size to high ages. In contrast, common and internal carotid arteries with elevated intima-media thickness (>/=50th percentile) experienced marked age-dependent dilation that started already in the 5th decade and continuously accelerated thereafter (structural ageing). Vessel diameters were subject to complex regulation involving morphometric characteristics, sex, wall thickness, hypertension, LDL cholesterol levels, and alcohol consumption. Vascular remodelling secondary to incident or slowly progressive (mural) atherosclerosis included local compensation and a generalised dilation response of vascular segments not primarily affected. Adaptive enlargement at the site of active atherogenesis effectively preserved a near-normal lumen in most instances. The current study identified a second main type of plaque growth, characterized by episodic marked increase in lesion volume probably on the basis of plaque thrombosis. In this setting, we did not observe maximum but insufficient compensation but instead usually observed no compensation at all. Failure of vascular remodelling and marked expansion in plaque size acted synergistically in producing significant lumen compromise. The current prospective survey describes fundamental principles and various facets of arterial remodelling and vascular biology in the general population (in vivo). Vessel geometry was subject to marked temporal changes and showed a correspondingly complex (multifactorial) and dynamic regulation. Vascular remodelling emerged as an important compensatory process in human atherogenesis, which crucially contributed to the determination of lumen obstruction. Efficacy and failure of compensation primarily depended on the type and pathomechanisms of underlying atherogenesis and only in second instance on plaque size and location.