Sjögren's syndrome is a systemic autoimmune disease that frequently presents concomitantly with other systemic connective tissue or organ-specific autoimmune diseases. This association is well described for systemic lupus erythematosus and rheumatoid arthritis. The presence of Sjögren's syndrome influences the expression of the other autoimmune disease to some degree, for instance by increasing fatigue and lymphoma risk. The etiopathogenic mechanism for the simultaneous or sequential development of multiple autoimmune diseases in one individual is not well understood. Common genetic backgrounds and additional immunogenetic, environmental, or hormonal factors may be responsible for the formation of subsets of autoimmune disease clustering. While the most currently accepted classification criteria (American European Consensus Criteria) designate these cases as secondary Sjögrens syndrome, the terms overlapping or associated Sjögren's syndrome are frequently used in the literature to describe these cases.