Systemic lupus erythematosus (SLE), also called lupus, is an autoimmune disorder in which the body's immune system (the cells in the body that fight infection) incorrectly attacks the body's own tissues and organs, leading to inflammation and damage. Lupus most commonly affects women of childbearing age but also occurs in children, adolescents, and men. The cause of lupus is unknown, but it has been associated with genetic, environmental, and infectious causes. The disorder may affect almost all organs in the body. It may be mild in some cases (for example, involving only the skin) and very severe in other cases (affecting multiple organs, including the brain). The disease course is characterized by flares (intervals of active disease) and remissions (intervals of inactive disease). This Patient Page is based on one published in the June 22/29, 2005, issue of JAMA.