Gastrointestinal stromal tumors(GISTs)usually develop in the stomach and small intestine and only rarely occur at the ampulla of Vater,with only 11 cases reported in the literature.We report a case of a GIST of the ampulla of Vater.A 36-year-old,previously healthy man presented with a loss of consciousness lasting a few minutes.A gastroduodenal endoscopy revealed a submucosal tumor with central ulceration at the ampulla of Vater.The enhanced computed tomography scan revealed a smooth-outlined hypervascular solid mass(24 mm×30 mm)in the second part of the duodenum.Neither lymphadenopathy nor metastasis was observed.Magnetic resonance cholangiopancreatography and endoscopic retrograde cholangiopancreatography showed normal bile and pancreatic ducts.Biopsies were collected from the ulcerative lesion,and the tumor was diagnosed as a GIST.A submucosal tumor with central ulceration may be a characteristic form of GISTs of the ampulla of Vater,and biopsy studies are useful for the diagnosing such tumors.The patient underwent pancreatoduodenectomy,and the operative specimen revealed a 2.2-cm GIST with 1 mitosis per 50 highpower fields.The gold standard for treatment of GISTs is surgical resection without rupture of a capsule.If technically possible,local resection may be considered.However,when the location of the lesion presents challenges,a pancreatoduodenectomy should be performed for GIST of the ampulla of Vater. Gastrointestinal stromal tumors (GISTs) usually develop in the stomach and small intestine and only rarely occur at the ampulla of Vater, with only 11 cases reported in the literature. We report a case of a GIST of the ampulla of Vater. A 36-year -old, previously healthy man presented with a loss of consciousness lasting a few minutes. A gastroduodenal endoscopy revealed a submucosal tumor with central ulceration at the ampulla of Vater. The enhanced computed tomography scan revealed a smooth-outlined hypervascular solid mass (24 mm × 30 mm) in the second part of the duodenum. Neither lymphadenopathy nor metastasis was observed. Magnetic resonance cholangiopancreatography and endoscopic retrograde cholangiopancreatography showed normal bile and pancreatic ducts. Biopsies were collected from the ulcerative lesion, and the tumor was diagnosed as a GIST. A submucosal tumor with central ulceration may be a characteristic form of GISTs of the ampulla of Vater, and biopsy studies are useful for the diagnosing such tumors. The patient underwent pancreatoduodenectomy, and the operative specimen revealed a 2.2-cm GIST with 1 mitosis per 50 highpower fields. the gold standard for treatment of GISTs is surgical resection without rupture of a capsule. If technically possible, local resection may be considered.However, when the location of the lesion presents challenges, a pancreatoduodenectomy should be performed for GIST of the ampulla of Vater.