Seven patients with multiple myeloma who developed a second neoplasm are presented. There were four patients with acute leukemia and three patients with non-hematologic neoplasms. The patients with acute leukemia were among the longest survivors (median duration ≈ 72 months) and the response to anti-leukemic therapy in these patients was generally poor. Of the three patients with non-hematologic neoplasms, one patient was observed with simultaneous renal cell carcinoma and the other two patients developed adenocarcinoma of the colon and lung subsequently. In addition, two patients with mammary carcinoma who subsequently developed multiple myeloma were included. Literature was reviewed and the possibility that multiple myeloma itself might be a risk factor for the development of other malignancies was discusse