Abstract: The obstetrician-gynecologist often is the physician who first encounters a patient with new symptoms and signs of an autoimmune disease. A basic understanding of autoimmune diseases is particularly useful for the obstetrician-gynecologist because autoimmune diseases are more prevalent in women, pregnancy can modulate the activity of preexisting disease, and the postpartum period can affect risk of new onset disease. Moreover, recent observations offer a new perspective on the interface of pregnancy and autoimmune disease. Long-term persistence of cells that trafficked between child and mother during pregnancy has been implicated in some autoimmune disorders. Familiarity with the multiple and varied presentations of these diseases and with the interpretation of screening test results can assist the obstetrician-gynecologist in identifying an autoimmune disease, counseling the patient, and implementing an initial treatment plan.