Mikulicz's disease represents a unique condition involving enlargement of the lacrimal and salivary glands. Mikulicz's disease has been considered part of primary Sjögren's syndrome because both diseases were histologically similar. However, the gland swellings in Mikulicz's disease are persistent, and its decreased secretional function is good responsiveness to glucocorticoid. Serologically, Mikulicz's disease is characterized by few autoantibody including anti-SS-A and anti-SS-B antibodies. Recently, it is revealed elevated IgG4 concentrations in the serum and prominent infiltration by plasmacytes expressing IgG4 in the lacrimal and salivary glands in Mikulicz's disease. Prominent IgG4-positive plasma cells are also detected in systemic lymph tissues. We cannot detect the phenomenon in Sjögren's syndrome. In complications with Mikulicz's disease, there are autoimmune pancreatitis, retroperitoneal fibrosis, tubulointerstitial nephritis, autoimmune hypophysitis, Riedel's thyroiditis, which are related to IgG4 in its pathogenesis. Mikulicz's disease is different from Sjögren's syndrome, and may be a systemic IgG4-related plasmacytic disease.