Although thrombotic thrombocytopenic purpura (TTP) has been described in patients with systemic lupus erythematosus (SLE), the relationship between these 2 diseases is controversial. We recently treated a patient with longstanding SLE who developed TTP. The patient responded to therapy with aggressive plasmapheresis. Review of the literature revealed that TTP may occur in the setting of either active or inactive SLE. Survival in SLE associated TTP correlated with the use of plasma therapy (plasma infusion or plasmapheresis) rather than with the activity of the underlying autoimmune disease. We conclude that TTP and SLE represent distinct clinical entities that may occur together in an immunologically predisposed host. The use of plasma therapy appears to have had a significant impact on survival in these patients.