CD56 (NCAM), a neural adhesion molecule, is normally expressed on natural killer cells and subsets of T cells and is commonly seen on hematolymphoid neoplasms such as plasma cell myeloma and acute myelogenous leukemia. It is uncommon in B-cell lymphoma. From 2001 to 2003 a cohort of 20 cases of CD56 B-cell lymphomas was identified by flow cytometry (<0.5% of all B-cell lymphomas studied) during a 2-year period. Most (90%) expressed CD10 and 5/5 tested cases were BCL6, suggesting a follicular origin. An extranodal disease presentation was seen in 45% and may be related to CD56 expression. These CD56 B-cell lymphomas may represent a new subset of large B-cell lymphoma. The relationship of cells with this antigenic profile to normal B-cell differentiation is explored.