Several patterns of association between Hodgkin and non‐Hodgkin lymphomas are recognized, some of which support a common cellular origin or shared transformation events for both malignancies. We describe the U‐2940 cell line derived from a diffuse large B‐cell lymphoma with some features consistent with mediastinal large B‐cell lymphoma, clinically apparent 1 month after the initial course of chemotherapy for Hodgkin's disease, fulfilling the criteria for composite malignancies. U‐2940 cells display a mature B phenotype with hypermutated IgH rearrangement typical of germinal/postgerminal center origin. The cell line is negative for Epstein‐Barr virus and no evidence of t(14;18) was found. U‐2940 cells display multiple chromosomal rearrangements similar to recurrent aberrations described in both Hodgkin and non‐Hodgkin lymphomas, also partially shared by U‐2932 derived from a B‐cell lymphoma sequential to Hodgkin's disease. The original large B‐cell lymphoma and the U‐2940 cell line bear microsatellite instability, an abnormality associated with particular subtypes of non‐Hodgkin lymphomas and found in tissues involved by Hodgkin lymphoma. Therefore, U‐2940 cells bear several features known to occur in Hodgkin and in non‐Hodgkin lymphomas, leading to the assumption that this cell line may constitute a useful tool to address elective pathways of lymphomagenesis and eventually the Hodgkin and non‐Hodgkin lymphoma association. © 2005 Wiley‐Liss, Inc.