Chronic periaortitis is a local complication of human atherosclerosis. It is defined as the triad of advanced atherosclerosis, medical thinning and aortic adventitial chronic inflammation. It is present to a variable degree in association with atherosclerotic abdominal aortic aneurysms. These aortic adventitial infiltrates differ from those described solely within the atheroma itself, in that they consist predominantly of B lymphocytes. Many of the lymphocytes are activated and proliferating, and germinal centres are common. In this study, an immunohistochemical analysis was carried out on fresh surgical aortic aneurysm tissue in order to investigate the presence and distribution of activation-inducible adhesion molecules, and to correlate this with the degree of inflammation. A consistent finding was the presence of E-selectin on endothelial cells in up to 50% of the vessels throughout the aortic wall and at the base of the atheroma, independent of the severity of inflammation. ICAM-1 expression was abundant on many cell types and increased with the severity of chronic inflammation, being strongest in the germinal centres. VCAM-1 expression was predominant on follicular dendritic cells and also increased with severity of inflammation. VCAM-1 expression was also detected on vessels within lymphoid follicles. The pattern of expression of the adhesion molecules suggests a role in the initiation and progression of chronic inflammation associated with advanced atherosclerosis.