A 45-year-old woman was found to have a pancreatic tumor by abdominal ultrasound performed for a medical check-up. Abdominal contrast-enhanced computed tomography showed a hypovascular tumor measuring 30 mm in diameter in the pancreatic tail. Endoscopic ultrasound-guided fine needle aspiration was performed. An extragastric growing gastrointestinal stromal tumor was thereby diagnosed preoperatively, and surgical resection was planned. Laparoscopic surgery was attempted but conversion to open surgery was necessitated by extensive adhesions, and distal pancreatectomy, splenectomy, and partial gastrectomy were performed. The histological diagnosis was an intra-abdominal desmoid tumor. A desmoid tumor is a fibrous soft tissue tumor arising in the fascia and musculoaponeurotic tissues. It usually occurs in the extremities and abdominal wall, and only rarely in the abdominal cavity. We experienced a case with an intra-abdominal desmoid tumor that was histologically diagnosed after laparotomy, which had been preoperatively diagnosed as an extragastric growing gastrointestinal stromal tumor. Although rare, desmoid tumors should be considered in the differential diagnosis of intra-abdominal tumors. Herein, we report this case with a literature review.