Sjögren's syndrome (SS) is a progressive autoimmune rheumatic disorder. Its precise etiology is unknown, although several contributing factors have been identified. One theory is that the condition results from complications related to infection with the Epstein-Barr virus. Primary exposure to or reactivation of Epstein-Barr virus elicits expression of the human leukocyte antigen complex. This is recognized by T lymphocytes (CD 4+) resulting in the release of cytokines (tumor necrosis factor, interleukin-2, interferon-gamma, and others). A genetic marker specific for Sjögren's syndrome, HLA-DR4, has been identified. According to the World Health Organization, the prevalence of Sjögren's syndrome is unknown. A recent epidemiologic study in Sweden estimated the prevalence in the adult population to be 2.7%. In the United States, 10 years ago, the number of patients with Sjögren's syndrome was thought to be fewer than 100,000. This number today is estimated to be more than 1 million. Sjögren's syndrome has been reported in nearly every major country of the world, and the geographic distribution of cases appears to be relatively uniform. Sjögren's syndrome typically affects women (90%) during the fourth or fifth decade of life. Isolated cases of Sjögren's syndrome in children have been reported.