The anatomy of the vasa vasorum of the carotid arteries was assessed by light and electron microscopy in a series of 25 New Zealand White male rabbits. The low viscosity acrylic resin, LR White, was used to cast the microvasculature. The carotid artery was found to have an endothelial monolayer placed directly upon a broad fenestrated internal elastic lamina. The media consisted of 12-18 laminae comprised of smooth muscle cells, elastin, collagen and ground substance. Vasa vasorum were confined to the adventitial layer, with no penetration into the media. They arose directly from the lumen of the carotid artery in addition to the arterial branching points. The potential role of the vasa vasorum in the aetiology of atherosclerotic plaques is discussed.