Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease that has a broad range of clinical manifestations. In SLE, tissue damage in multiple organs is caused by autoantibodies and immune complexes. Because other autoimmune diseases, infectious diseases, central nervous system diseases, and fibromyalgia can also manifest with multisystem disease involvement, these other conditions need to be considered when considering a diagnosis of SLE.