Sjögren's syndrome (SS) is a chronic organ-specific autoimmune disease characterized by lymphocytic infiltration into the salivary and lacrimal glands. About half of primary SS patients develop systemic disorders. Primary SS can be divided into three stages according to the extent of organ damage and the course of the disease. In stage I, (approx. 45% of cases), patients have only sicca syndrome and do not experience any systemic involvement, even after 10 years. In stage II (approx. 50% of cases), patients experience lymphocytic organ damage, which may involve the pulmonary, renal, hepatic, hematologic, and/or dermatologic systems, among others. Finally, in stage III (approx. 5% of cases), patients develop malignant lymphomas. Lymphomas in salivary glands are thought to arise from lymphoepithelial lesions in which there are close interactions among epithelial cells, T cells, and B cells. The B cells in the lesions become activated through the interaction between CD40L and CD40. The progression from polyclonal lymphoproliferation to monoclonal lymphoproliferation, to mucosa-associated lymphoid tissue (MALT) lymphoma, and finally to high-grade malignant lymphoma is regarded as a multi-step process. Antigenic activation of B cells, together with oncogenic events, including p53 inactivation and bcl-2 activation, may play important roles in B cell monoclonal proliferation and malignant transformation. The rheumatoid factor clone is regarded as a candidate B cell clone that undergoes transformation.