ICAM-1 is an immunoglobulin-like protein expressed on the surface of several cell types including endothelial cells and cells involved in the immune response. It plays an important role in the adhesion and migration of leukocytes to the sites of inflammation. ICAM-1 is expressed as membrane-bound and soluble form. The latter was detected in blood serum and cerebrospinal fluid in the course of infectious, autoimmune as well as proliferative diseases. This article describes the role of ICAM-1 in the pathogenesis of various disease entities and its clinical significance.