Thrombotic thrombocytopenic purpura (TTP) is a rarely seen complicating systemic lupus erythematosus (SLE). The diagnosis of TTP in a setting of SLE is challenging since both share common features including thrombotic microangiopathy. We report two cases of SLE with TTP one with a good response when cyclophosphamide was given early with plasmapheresis and steroids; the other with a poor outcome in a patient given cyclophosphamide late in the course of the disease.