A complicated unresectable desmoid tumor is a life threatening disease. An unresectable desmoid tumor with perforation of the small bowel, was experience at my institute. In this case, the desmoid tumor had invaded major vessels, so that complete resection of the tumor would necessitate resection of most of the small bowel. A desmoid tumor with perforation of the small bowel following ileal pouch anal anastomosis for familial adenomatous polyposis is rare. If the patent had not undergone the operation, they would not have survived. Also, had the tumor with a perforated bowel been completely, resected, they also would not have survived. Therefore, a partial resection of the desmoid tumor and perforated small bowel was performed, with a good result. It is not necessary to abort such an operation, with potentially fatal consequences, due to an unresectable desmoid tumor with a perforated small bowel. Herein, this case is reported with a review of the literature.