Immunoglobulin (Ig) G4-related systemic disease is a recently characterized entity. The best-known manifestation is pancreatitis. Other systemic involvements are also described. Three cases of this disease with hypophyseal involvement have been reported in the literature, all diagnosed clinically. We herein present the first case of IgG4-related hypophysitis diagnosed histopathologically. The patient is a 77-year-old Chinese man with a pituitary tumor. Histologic examination of the resected tumor showed hypophysitis with features of inflammatory pseudotumor. Clinical review showed history of pancreatitis and cholecystitis 4 years ago. The pancreatic biopsy and gall bladder specimens obtained previously had the same pathologic features of inflammatory pseudotumor. Immunohistochemistry highlighted abundant IgG4-positive plasma cells in all 3 specimens. Serum IgG4 level was also elevated. A diagnosis of IgG4-related systemic disease was confirmed. This is the first case of intracranial inflammatory pseudotumor shown to be associated with IgG4-related systemic disease.