A woman was admitted to the hospital with joint pain. She was also found to have pericardial effusion, renal dysfunction, pancytopenia, and positive antinuclear antibody; a diagnosis of systemic lupus erythematosus (SLE) was made. Although she had neither neurological symptoms nor fever, laboratory tests showed microangiopathic hemolytic anemia, thrombocytopenia, and renal dysfunction. Therefore, we diagnosed her illness as SLE complicated by thrombotic microangiopathy (TMA). Plasmapheresis was performed in addition to immunosuppressive therapy. TMA improved rapidly and renal function improved gradually. The number of patients with SLE complicated by TMA is relatively small and the mortality rate is extremely high. A diagnosis of TMA is difficult to determine in patients with SLE because of the overlapping clinical symptoms. The data suggest that prompt induction of plasmapheresis in addition to immunosuppressive therapy is necessary in SLE patients having symptoms suspicious of TMA even before they fulfill the 5 symptoms typical of TMA.