Two patients with plasma cell dyscrasia and IgG lambda paraproteinemia in association with the rare disorder, chronic neutrophilic leukemia (CNL), are described. Cytogenetic studies excluded Philadelphia + chronic myeloid leukemia and molecular analysis of the breakpoint cluster region (bcr) revealed no evidence of clonal gene rearrangement. Nine similar cases of coexistent CNL and paraproteinemia have been identified in the literature and attention is drawn to the disproportionate excess of lambda light chain restriction in this subset of patients. Evidence supporting a clonal origin of CNL is considered and the nature of the relationship between the chronic myeloid expansion and the development of multiple myeloma is discussed.