The immune pathogenesis of idiopathic thrombocytopenic purpura (ITP) is well established; however, the diagnostic criteria do not require identification of platelet autoantibodies. The abundance of methods devised for the measurement of platelet antibodies over the years provides evidence of the so-far futile search for a reliable diagnostic assay. The latest generation of platelet antigen-specific assays has widened the knowledge of autoimmune mechanisms in thrombocytopenia, but they still lack sufficient sensitivity to be a useful tool in the routine evaluation of thrombocytopenic patients.