The study presented a case of 56-year-old male who underwent emergency surgery due to massive upper gastrointestinal bleeding. Prior to surgery, during the last two years the patient was hospitalized and diagnosed several times due to recurrent gastrointestinal bleeding. During the last duodenoscopy a presence of pancreatic tumor infiltrating distal part of the duodenum was shown. The patient was released home - further treatment was postponed until results of histological examination of biopsy were available. Before that the patient was admitted and underwent surgery in our hospital due to massive gastrointestinal bleeding. During surgery no pancreatic or duodenal tumor was found. We revealed a neoplasmatic tumor of small intestine, localized about 7-10 cm to Treitz' ligamentum. Resection of the intestine was performed. The postoperative course was uneventful. The histological examination of the specimen revealed an isolated extramedullary plasmocytoma of the small intestine.