The remission rate with plasma exchange (PE) in thrombotic thrombocytopenic purpura (TTP) exceeds 80%, but the disease relapses in up to 20-30% of the cases. Clinical characteristics and response to treatment of relapsed TTP are not well defined. The objective of the present study was to compare the clinical and biological characteristics at presentation and the response to treatment between de novo and relapsed TTP. For such purpose, a total of 102 episodes of idiopathic TTP (70 de novo and 32 relapses) included in a recent multicentric prospective cohort study were analysed. All patients were homogeneously treated with daily PE and costicosteroids. In comparison with de novo TTP, episodes of relapsed TTP showed a higher Hb level (median, 122 g/l versus 91 g/l, p < 0.001) and lower serum lactate dehydrogenase (2.2- versus 4.5-fold above the upper limit of normality, p < 0.001). Neurological symptoms and fever were less frequently observed in patients with relapsed TTP than in patients with de novo TTP. Patients with relapsed TTP needed fewer PE sessions (five versus ten, p = 0.02) and a smaller volume of plasma (221 ml/kg versus 468 ml/kg, p = 0.004) to achieve remission than those with de novo TTP. There was no significant difference in the rate of recrudescence under treatment, the need of complementary treatments or the frequency of refractoriness to PE therapy. In conclusion, relapsed TTP has a milder clinical profile and responds more easily to PE than de novo TTP.