Sjögren's syndrome (SS) is chronic autoimmune disease characterized by destructive lymphocyte infiltration of salivary and lacrimal glands, which results in dry eyes and dry mouth. Despite extensive study of the underlying cause of SS, the pathogenesis remains obscure. The Sjögren's International Collaborative Clinical Alliance (SICCA) by five Research Groups located in Argentina, China, Denmark, the United States and Japan, is the first registry and clinical data-specimen repository to establish the International Standard Criteria for diagnosing SS. Patients with SS have a relative increased risk for development of B cell lymphoma compared with other autoimmune rheumatic diseases. We discuss the possible mechanisms for lymphoma development. The topics concerning SS is IgG4-related lymphoproliferative diseases, such as Mikulicz's disease and autoimmune pancreatitis. Based on the analysis of patients registered from all over Japan, we propose a new clinical entity IgG4-positive multi-organ lymphoproliferative syndrome (IgG4+ MOLPS).