Isoforms of the transmembrane glycoprotein CD44, generated by alternative RNA splicing, have been correlated to tumor dissemination. For evaluation of the potential role of CD44 variant isoforms in non- Hodgkin's lymphoma (NHL), the presence of CD44 isoforms was analyzed in a large panel of reactive and neoplastic lymphoid tissues by immunohistochemical staining, as well as detection of CD44 variant RNAs by the reverse transcriptase-polymerase chain reaction. Whereas the CD44 standard or hematopoietic isoform (CD44s), devoid of the variant regions, was expressed in all leukocyte subpopulations, the variant isoforms (CD44v) showed a highly restricted pattern of expression, mainly observed in epithelial layers of lymphoid tissues and subpopulations of leukocytes after stimulation. In addition to a strong expression of CD44s, variant isoforms containing CD44–6v in combination with other variant exons were observed predominantly in aggressive lymphoma and were associated with a shorter overall survival of patients (n = 138; P < .0001). Moreover, multivariate analysis indicated CD44–6v as a new independent prognostic parameter in high grade NHL in comparison with the risk groups defined by the International NHL Lymphoma Prognostic Factors Project (N Engl J Med 329:987, 1993).