A rare case of follicular dendritic cell (FDC) sarcoma is reported. A 71-year-old woman was admitted for evaluation of constipation. Computerized tomography showed cervical, supraclavicular, retroperitoneal, and paraaortic lymphadenopathies. Histological findings from a cervical lymph node revealed Hodgkin's disease at first. But tumors that arose both in the cervical and the left interscapular regions during the chemotherapy were immunohistochemically confirmed to be of follicular dendritic cell origin. The ultrastructural findings were consistent with those of FDC sarcoma. FDC sarcoma is a rare nonlymphoid cell-derived malignant tumor originating from the lymphoid tissue. The diagnosis of FDC sarcoma is most accurately established by immunohistochemical methods, using its specific markers.