The patient was a 22-year-old woman with FAP, who had undergone laparoscopic total colectomy 3 years previously. She presented to our hospital with a high fever and abdominal pain. Large hard tumors were palpated in the right lower abdomen and pelvis. Blood examination showed an inflammatory response. CT scan revealed 17 cm diameter solid tumors. At surgery, 2 tumors arising from the mesentery of the small intestine were found, neither of which invaded any organs. We performed tumor extirpation with partial resection of the duodenum, ileum, right fallopian tube and rectum. A jejunal stoma was formed, leaving a length of remnant intestine of about 120 cm. The histopathological diagnosis was given as desmoid tumor with infection. The patient was discharged from the hospital on the 9th postoperative day. Desmoid tumor is the second most common cause of death in FAP patients. Although desmoids can also occur in the extremities, most FAP patients develop intra-abdominal tumors. Despite being histologically benign, they are locally infiltrative and can cause death through invasion and destruction of adjacent vital structures and organs. Here, we report a case of desmoid tumors with FAP with reference to the literature.