A multiple myeloma patient presented for cytogenetic analysis at diagnosis of secondary MDS, which followed cytotoxic treatment including melphalan. Two abnormal unrelated clones were detected, one of them had 5q-, 7q- with clonal evolution of an additional aberration, t(12;13); in the second clone there was a translocation between the two homologues of chromosome 1 as the only aberration. We suggest that the clone with 5q- and 7q- represented the secondary MDS cells, whereas the abnormal clone with t(1;1) represented the plasmablasts of the multiple myeloma.