RESUMEN
Plasmacytoma is a lymphoid neoplasm with the histological, immunological, and functional features of an immunoglobulin- secreting B cell proliferation. Intestinal involvement may be a manifestation of a diffuse multiple myeloma or less commonly, a primary tumor. Gastric plasmacytomas occur more frequently than intestinal plasmacytomas. We experienced a woman who had a primary extramedullary plasmacytoma that originated in the sigmoid colon. She had suffered from abdominal pain and diarrhea for 4 months and underwent a colonoscopy examination. A colonoscopic biopsy revealed it to be ulcerative colitis, and she underwent a total colectomy as a result. However, the permanent biopsy finding was a plasmacytoma. We review the clinical manifestations, as well as the radiological and histopathological findings of a plasmacytoma.