3 cases of desmoid tumours of the mesentery occurring as part of Gardner's syndrome are reported. In 2 cases, CAT scanning was carried out. We underline the value of this examination compared to other imaging methods. It allows the establishment of a diagnosis, investigation for complications, the operability to be assessed and is useful for monitoring patients. Its major value is in avoiding an unnecessary laparotomy, a factor certain to produce recurrence, in certain patients. Other alternative therapy may then be proposed.