To determine whether primary lymph node plasmacytoma (PLNP) is a distinct entity among other types of plasma cell neoplasia, we analyzed a large series of PLNPs from 2 large lymphoma registries to compare histologic, immunophenotypic, and clinical features of PLNPs, nonnodal extramedullary plasmacytomas, and multiple myeloma. Twenty-five PLNPs (clinical data on 15 cases) were compared with 10 non-lymph node plasmacytomas and 51 cases of multiple myeloma; 36 cases of reactive plasmacytoses were used as controls. The histologic features of PLNP and other extramedullary plasmacytomas were similar. The histologic features of PLNPs were more immature than those of reactive plasmacytoses and less immature than in multiple myeloma. The immunophenotype of PLNPs significantly differed from that of reactive plasmacytoses, other extramedullary plasmacytomas, and multiple myeloma. PLNPs did not progress to multiple myeloma, unlike other extramedullary plasmacytomas, even though survival in PLNPs and other extramedullary plasmacytomas was similar. Our findings suggest that PLNPs may be distinct from other plasma cell dyscrasias.