Cortactin, an actin binding protein and Lyn substrate, is up-regulated in several cancers and its level is associated with increased cell migration, metastasis and poor prognosis. The identification that the Src kinase Lyn and its substrate HS1 are overexpressed in B cell chronic lymphocytic leukemia and involved in resistance to chemotherapy and poor prognosis, prompted us to investigate the role of cortactin, an HS1 homolog, in the pathogenesis and progression of this disorder. In this study we observed that cortactin is overexpressed in leukemic cells of patients (1.100.12) with respect to normal B lymphocytes (0.19+/-0.06, p=0.0065). Fifty-three % of our patients expressed the WT mRNA and p80/85 protein isoforms, usually lacked in normal B lymphocytes which express the SV1 variant and the p70/75 protein isoforms. Moreover, we found an association of the cortactin overexpression and negative prognostic factors, including ZAP-70 (p<0.01), CD38 (p<0.01) and somatic hypermutations in the immunoglobulin heavy-chain variable region (p<0.01). Our results show that patients with B cell chronic lymphocytic leukemia express high level of cortactin with a particular overexpression of the WT isoform that is lacking in normal B cells, and a correlation to poor prognosis of patients, suggesting that this protein could be relevant in the pathogenesis and aggressiveness of the disease.