有一群和第四型免疫球蛋白G相關的疾病目前被廣泛的討論，其中最常見的就是第一型自體免疫性胰臟炎。第一型自體免疫性胰臟炎經常表現出阻塞性黃疸及胰臟腫大。我們報告一個罕見的病例是以上腹痛及胰臟腫瘤來表現，開刀後病理檢查才證實是第一型自體免疫性胰臟炎。此外，放射線檢查也發現病人的腹主動脈有一段管壁有明顯增厚，證實有主動脈炎。這個病例提醒我們當病人出現不尋常的胰臟腫瘤，自體免疫性胰臟炎必須要當作是鑑別診斷之一。

IgG4-related diseases (IgG4-RD) are a spectrum of diseases involving many organs. Type 1 autoimmune pancreatitis is the most common disease of IgG4-RD. It often presents with obstructive jaundice and swelling of the pancreas. We report a case of a 56-year-old male with initial presentation of epigastric pain. Endoscopic abdominal sonogram, CT scan and MRI revealed a tumor over pancreatic tail. Pancreatectomy was done and the pathological report revealed IgG4-related autoimmune pancreatitis. In addition, wall thickening of the infra-renal abdominal aorta was also noted, and aortitis was diagnosed. The case emphasizes autoimmune pancreatitis be present with a pseudotumor and complete studies like IgG subclasses, including IgG4, should be included. (J Intern Med Taiwan 2015; 26: 169-173)