It is not uncommon for some B-lineage non-Hodgkin lymphomas (NHLs) to aberrantly coexpress T-cell markers, particularly CD5, as well as CD7, CD2, CD4, and/or CD8 in rare cases. Cases of CD3-positive B-cell NHL, however, have not previously been described in the literature. We present 4 cases of large B-cell lymphoma aberrantly coexpressing T-cell marker CD3 and B-lineage markers as well as demonstrating clonal rearrangement of the immunoglobulin genes but not the γ T-cell receptor gene. To our knowledge, this represents the first series report of B-cell NHL coexpressing T-lineage–specific marker CD3. The identification of such cases indicates that the use of CD3 antibody alone in paraffin sections may lead to an incorrect determination of cell lineage in some B-cell NHL. Immunohistochemistry using additional cell lineage specific markers or molecular analysis for antigen receptor gene rearrangements are necessary for correct determination of the cell lineage in such cases.