The authors describe a case of a young patient, who underwent a by-pass surgery for ileus of the small intestinal loops due to a wide-spread tumor of the mesentery, conducted in a different hospital. The patient was then re-operated in the Faculty hospital in Plzen, the tumor was successfully removed en-block and the pathologist came to a conclusion and diagnosed mesenterial fibromatosis. The case is being discussed from the point of view of the rarely occurring intraabdominal fibromatosis.