Intravascular large B-cell lymphoma (IVLBCL) is a rare disease entity of non-Hodgkin lymphoma according to the current WHO classification. This rare form of B-cell lymphoma is characterised by selective growth of tumour cells in the lumina of small vessels of various organs. Strange characteristics of IVLBCL, including the absence of marked lymphoadenopathy and the usually aggressive clinical behaviour, result in the delay of timely and accurate diagnosis and fatal complications. Thus, the prognosis of IVLBCL is extremely poor. The success achieved with the anti-CD20 chimeric monoclonal antibody, rituximab, represents an important milestone in the clinical practice of B-cell lymphoma. An advantage of adding rituximab to conventional chemotherapies has been shown, in the process of increasing our understanding of the clinical and pathological manifestations for IVLBCL. This Review describes the cutting edge of research on IVLBCL, and discusses the unsolved issues from biological and clinical perspectives to provide a better understanding of this rare lymphoma.