The Oklahoma thrombotic thrombocytopenic purpura-hemolytic uremic syndrome (TTP-HUS) Registry, an inception cohort of 382 consecutive patients with TTP-HUS, provides a complete community perspective of these syndromes. TTP, as defined by thrombocytopenia and microangiopathic hemolytic anemia without an alternative etiology, is the appropriate term for all adults. These limited diagnostic criteria are supported by the presenting features of patients with ADAMTS13 deficiency, in whom both neurologic and renal abnormalities are uncommon. HUS is the appropriate term for children who fulfill these diagnostic criteria and who also have renal failure. These definitions are consistent with current management: plasma exchange is the essential treatment for most adults; supportive care is sufficient for children with HUS. Plasma exchange treatment has decreased the mortality of TTP from 90 to 10%. Patients with acquired autoimmune ADAMTS13 deficiency may also require immunosuppressive treatment to achieve a durable remission. Recovery has revealed previously unrecognized long-term risks. Recurrent acute episodes occur in approximately 40% of patients with acquired ADAMTS13 deficiency; most relapses occur within the first year and most patients have only one relapse. Adults with TTP of any etiology have a high risk for persistent minor cognitive abnormalities.