We report one case of primary acute myelogenous leukemia (AML) and one case of refractory anemia with excess blasts in transformation (RAEB-T) each presenting concomitantly with multiple myeloma, an unusual finding. The twin diagnoses in each patient were confirmed by cytochemical and immunohistochemical studies, and in one of our cases, by ultrastructural, flow cytometric, and molecular studies. The last three methods have not been previously used to document this phenomenon.