A case of plasmacytoma of the ovary and breast, which developed in a patient with a solitary plasmacytoma in the lumbar vertebra for nine months, was diagnosed cytologically and histologically. Enlargement of the right ovary and multiple palpable masses in the right and left breast were already present at six months after the diagnosis of vertebral solitary plasmacytoma. At eight months, plasma cell leukemia developed, and nine months the enlarged both ovaries, replaced by yellowish-gray solid tumors showed infiltration of immature plasma cells. The cytologic features of the ovarian tumors were same with those of the breast tumor. The tumor cells were of predominantly immature plasma cells with one or more nuclei. Some mature plasma cell had an eccentric nucleus with single nucleolus and peripherally clumped chromatin. Binucleated or multinucleated giant cells were often present. Histologically, sheets of poorly differentiated plasmacytoid tumor cells were separated by strands of hyaline fibrous tissue. On immunohistochemical stains, the tumor cells showed strong reactivity for lambda-light chain but no reaction for kappa-light chain, cytokeratin, or leukocyte common antigen.