In summary, plasma cell leukemia is a rare disorder that can develop spontaneously or evolve in patients with multiple myeloma. The diagnosis is based on laboratory features, including a plasmacytosis exceeding 2 X 10(9)/L or 20% of the differential cell count. Primary plasma cell leukemia should also be considered when fewer plasma cells are present provided that a clonal proliferation is documented. Most clinical characteristics are similar in both types of plasma cell leukemia. Lymphadenopathy and hepatosplenomegaly are more common in the primary form, and lytic bone lesions are more frequent in the secondary form. Patients with primary plasma cell leukemia may initially respond better to chemotherapy, including single agent drugs commonly used in multiple myeloma. However, resistant disease is expected, and most data suggest a median survival of less than 6 months in both types of leukemia. Because patients with primary plasma cell leukemia are in better condition, intensive chemotherapy and approaches such as bone marrow transplantation should be considered, especially in younger patients.