Systemic lupus erythematosus (SLE) is relapsing remitting autoimmune disease principally affecting the skin, joints, kidney, and serosal membranes (pleural, peritoneal). It is a fairly common disease (1:2500), principally affecting women (9:1 vs men) of childbearing age. The etiology of lupus is unknown but is likely multifactorial, resulting from genetic, immunological, and environmental factors that cause aberrant activation of the immune system and the production of autoantibodies (e.g. anti-nuclear antibodies to dsDNA and histones). Much of the injury due to lupus is caused by immune complexes formed between these antibodies and their antigens. These complexes deposit in blood vessels and glomeruli, resulting in acute necrotizing vasculitis and various forms of glomerulonephritis. The clinical picture of lupus can be highly variable and difficult to diagnose. The typical features include: butterfly rash on the face, fever, joint pain without deformity, pleuritic chest pain, and photosensitivity. Antiphospholipid antibodies are common in lupus patients, and are associated with a hypercoagulable state that can cause thrombosis (venous and arterial). Thrombosis and infarction of the placenta are common complications of pregnancy in lupus patients. Renal failure remains a common complication in lupus patients. Discoid and subacute cutaneous forms of the disease have skin disease only.