Anaplastic large cell lymphoma (ALCL) has been recognized recently as a distinct clinicopathologic entity, restricted to a subset of CD30-positive diffuse large cell lymphomas of T/null lineage. Some of the characteristic features of ALCL, such as CD30 antigen expression and the presence of large pleomorphic lymphoid cells infiltrating lymph node sinuses, can be found rarely in diffuse large B-cell lymphomas. We collected 11 such cases, and their clinical, morphologic, and immunophenotypic features are reviewed. The age of the patients ranged from 36 to 82 years (mean, 63.2 years) with a male to female ratio of 1:1.2. All neoplasms were nodal with a sinusoidal infiltrative pattern, although four neoplasms also had foci of confluent growth. Eight tumors were composed predominantly of large pleomorphic cells with occasional Reed-Sternberg-like cells. The other three tumors had a higher proportion of large monomorphic lymphoid cells. Necrosis and admixed granulocytes were other common features. Immunophenotypically, all cases were positive for CD30 and CD20 or CD79a. All eight cases examined for anaplastic lymphoma kinase-1 immunoreactivity were negative. In situ hybridization for Epstein-Barr virus RNA was performed in eight cases; two were positive. Excluding one consultation case with no available clinical follow-up data, six patients died of the disease within 3 years and one had disease relapse within 1 year. We conclude that an unusual variant of diffuse large B-cell lymphoma can closely mimic ALCL. However, these neoplasms can be distinguished from ALCL by virtue of their B-lineage and lack of anaplastic lymphoma kinase-1 expression. Evidence of Epstein-Barr virus infection can be found in a small subset of these neoplasms.