Two unusual, and perhaps causally related, clinical and cytogenetic features in a patient with Waldenström's macroglobulinemia are presented. Firstly, during the progression of the primary macroglobulinemia bone destruction and hypercalcemia occurred. Secondly, a t(1;3)(p36;q21) was found as the sole clonal chromosomal abnormality. This translocation is characteristic of acute myeloid leukemia (AML) and myelodysplastic syndromes with a high propensity for progressing to AML. The t(1;3) has previously never been reported in a lymphoproliferative disorder. Since the abnormality is associated with acute transformation of cells of the myelopoietic lineages, it is possible that the t(1;3), found in cells of lymphoid origin in the present case, not only induced the neoplastic process as such but also brought about the unusually malignant tumor progression.