We describe the association of 2 types of small B-cell lymphomas with different morphologic and immunophenotype patterns inside the same lymph node. Morphologically distinct zones were detected and studied with immunohistochemistry analyses. Most of the areas examined were characteristic of classic mantle cell lymphoma (CD20+, CD5+, cyclin D1+) with nodular and mantle zone areas. However, other areas had the morphologic and immunohistochemistry pattern of follicular lymphoma (CD20+, CD10+, Bcl2+). The diagnosis of both lymphomas was confirmed by polymerase chain reaction detection of both Bcl-1 MTC and Bcl-2 MBR rearrangements. DNA degradation in fixed tissue prevented a complete polymerase chain reaction analysis of immunoglobulin heavy chain rearrangements, but a single immunoglobulin H rearrangement was detected at the FR3 locus. These findings confirm the presence of a monoclonal cell population but do not demonstrate the same clonal origin for both lymphoma populations.