Diffuse large B cell non-Hodgkin's lymphomas (DLCL) form a heterogeneous group of tumors with diverse morphology, clinical features, treatment response and prognosis. The biological variables underlying this heterogeneity are unknown. In the present study, we explored the value of the lymphocyte homing receptor CD44, a putative determinant of lymphoma dissemination, in predicting prognosis in DLCL. Expression of the standard form of CD44 (CD44s) and of CD44 isoforms containing exon v6 (CD44v6) on tumor cells was assessed by immunohistochemistry in a cohort of 276 DLCL patients from a population based lymphoma registry. We observed that CD44s as well as CD44v6 expression correlated with tumor dissemination in patients with primary nodal DLCL. Importantly, in patients with localized nodal disease, CD44s was a strong prognosticator predicting tumor related death independent of the other parameters of the International Prognostic Index (IPI). Incorporation of CD44s in the IPI parameter 'stage', increased the prognostic value of this parameter in nodal DLCL. Our data identify CD44 as a biological prognosticator, which can be used to 'fine-tune' the IPI for nodal DLCL.