Mikulicz disease is a disorder characterized by symmetrical enlargement of the lacrimal and salivary glands. Beginning with the report by Morgan and Castleman2 in 1953, Mikulicz disease had been considered to be a subtype of primary Sjögren syndrome owing to their resemblance pathologically. However, later studies suggested that these 2 diseases were distinctly different pathologically and clinically, ie, in Mikulicz disease, lacrimal gland acinar cells maintained their function and were not programmed for cell death.3 More recently, Mikulicz disease has been suggested to be a disorder involving IgG4, the rarest subclass of IgG in healthy subjects. The serum level of IgG4 is elevated in patients with Mikulicz disease and prominent infiltration of IgG4-stained plasmacytes is observed pathologically, which are features not seen in Sjögren syndrome.1 Moreover, it has been proposed that Mikulicz disease belongs to the clinical entity IgG4-plasmacytic endocrinopathy, which includes IgG4-related sclerosing diseases such as autoimmune pancreatitis, sclerosing cholangitis, retroperitoneal fibrosis, and chronic sclerosing sialadenitis.4,5 These diseases are characterized by histopathological features that include dense lymphoplasmacytic infiltration intermixed with fibrosis, obliterative phlebitis, and prominent infiltration of IgG4-positive plasma cells. In IgG4-related chronic sclerosing sialadenitis, marked lymphoplasmacytic infiltration is associated with the destruction and atrophy of the salivary gland.5 These histopathological features are identical to those of the 4 cases of Mikulicz disease reported here. Another differential diagnosis would be extranodal marginal zone lymphoma of the mucosa-associated lymphoid tissue, which could, however, be excluded in all of the cases on the basis of histological and immunohistochemical findings of those lesions consisting of mature polyclonal lymphocytes and plasma cells. To our knowledge, no relationship between IgG4-related chronic inflammation and lymphoma of the mucosa-associated lymphoid tissue has been reported.