The coexistence of chronic lymphocytic leukemia (CLL) and multiple myeloma (MM) is rare, and there is no consensus about the clonal relationship of the two disorders when they occur in the same individual. We investigated chromosomal abnormalities in two patients with concurrent CLL and MM using interphase fluorescence in situ hybridization (FISH) with a panel of region-specific DNA probes. In patient 1, the clonal plasma cells harbored IgH translocations (14q32); however, FISH with probes for the four most frequent IgH partner genes in MM (CCND1, FGFR3, MAF, and MYC) did not detect translocations involving any of them. The CLL cells were characterized by deletions of 13q14, 11q23, and 17p13, as well as trisomy 12, none of which were found in the MM cells. In patient 2, deletions of 13q14 and 17p13 were detected in CLL cells, but no cytogenetic abnormalities were found in the MM cells. Both patients had relapsed MM following chemotherapy and had autologous stem-cell transplant, whereas their CLL has been stable and not requiring treatment. Our results show that the cytogenetic profiles differ between CLL and MM within the same patients, and provide evidence for two distinct malignant clones in both patients.