Immune thrombocytopenia (ITP) results in part from the presence of platelet antibodies, which can be demonstrated by the Monoclonal Antibody-Specific Immobilization of Platelet Antigens (MAIPA) assay. The aim of our study was to correlate the presence of antiplatelet autoantibodies and the natural history of ITP. We performed a retrospective, single-center study of 108 adults with newly diagnosed ITP who had indirect MAIPA assay performed at disease onset. Chronic ITP was defined by the presence of thrombocytopenia after 1 year. Bleeding diathesis was evaluated with a bleeding score. At baseline, patients with a positive indirect MAIPA have a greater bleeding score than patients with negative MAIPA assay [median (interquartile) = 8 (6-12) vs 2 (0-6), p = 0.002]. Patients with a positive indirect MAIPA also had a higher rate of chronic ITP (92.9 vs 68.7 %, p = 0.06). In multivariate analysis, a positive indirect MAIPA result and a platelet count at onset ≥10 × 10(9)/L remained independently associated with chronic ITP [adjusted OR (aOR) = 8.01; 95 % confidence interval (CI), 0.98-66.6; p = 0.05 and aOR = 3.09; 95 % CI, 1.18-8.10; p = 0.02, respectively]. Furthermore, when we analyzed together the results of direct (n = 41) and indirect MAIPA, the same results were observed. Thus, indirect MAIPA positivity at disease onset is associated with more severe hemorrhage and predicts a chronic course in adult ITP patients. MAIPA assay could be useful in the management of ITP patients when it is performed at diagnosis.