We report a 72-year-old man with sporadic intra-abdominal desmoid tumor manifesting as acute abdomen. CT scan revealed an air-containing tumor 7 cm in diameter; three weeks later, the tumor had shrunk to 4 cm on antibiotics. At surgery, a tumor arising from the transverse colon mesentery and infiltrating the jejunum was resected. No recurrence occurred over a 1-year follow-up.