A case of a 70-year-old man who first developed multiple myeloma and then chronic myelogenous leukemia (CML) within a 3-year period is documented. The patient, with monoclonal hypergammopathy, was diagnosed with smoldering myeloma with IgG-kappa and Bence Jones protein kappa paraproteinemia. No chemotherapy was given for the myeloma until progressive leukocytosis developed after approximately 3 years. This was found to be due to Philadelphia chromosome positive CML. A reverse transcription-polymerase chain reaction assay did not reveal BCR/ABL mRNAs when the myeloma was first diagnosed. The occurrence of 2 distinct hematologic malignancies in the same patient suggests either a different clonal evolution from a common pluripotent malignant stem cell since the CML stem cell also involves the B-lymphoid lineage, a coincident complication of the 2 hematological malignancies, or the coexistence of 2 distinct malignancies due to the same genetic background and/or exposure to similar carcinogenic agents. The literature provides support for the existence of a relationship between multiple myelomas and CML.