One case of polypoid solitary plasmacytoma in the sigmoid colon of a 60 year-old woman is presented. Plasmacytomas are rarely observed in the gastrointestinal tract and are especially uncommon in the côlon. Eight cases were published since 1972. They show a mean age of 46.3 years, a sex-ratio of 1/1, varying revealing symptoms, and no preferential colonic location. Two differential diagnosis must be discussed: an inflammatory pseudotumor, and a multiple myeloma related tumor. Multiple myeloma must be ruled out by a complete radiographic and biological research. Surgery is the only therapy described and seems to be efficient.