IgG4-positive plasma cell infiltration into multiple organs or tissues, such as the pancreas and salivary glands, associated with increased serum levels of IgG4 is a characteristic finding seen in IgG4-related disease. Affected organs may appear tumorous as a result of chronic inflammatory processes accompanied with progressive fibrosis. Recent cases of this disorder in which the pituitary gland was affected include cases of diffuse enlargement of the pituitary and/or its stalk associated with central diabetes insipidus and/or impaired anterior hormone production. Here we report two such cases, as well as two additional previously undiagnosed cases found in our database. In order to make a correct diagnosis of pituitary lesion involvement with IgG4-related disease, the clinical background and concomitant disorders should be carefully taken into consideration and the measurement of serum levels of IgG4 seems to be useful.