CD54/Intercellular Adhesion Molecule-1 (ICAM-1) is a cell adhesion molecule largely distributed among normal and neoplastic tissues. Through the binding to its ligand(s) CD54 plays a key role in cell to cell interactions leading to the immune response. Recently, CD54 expression has been investigated on hematopoietic cells: the antigen is predominantly expressed in the early stages of normal hematopoiesis and during the activation of blood cells. As regards to hematological malignancies, CD54 is strongly expressed on neoplastic cells from "stem cell derived" neoplasms. In AML, CD54 expression is related with other differentiation-linked molecules such as CD34 and HLA-DR and is significantly correlated with FAB morphological classification. In lymphoproliferative disorders, a high CD54 expression is associated with germinal centre lymphomas. This review summarizes our current understanding of CD54 with emphasis on recent advances and reference to unresolved issues such as its prognostic role in the clinical outcome of oncohematological diseases.