Idiopathic thrombocytopenic purpura (ITP) is a bleeding disorder. Thrombocytopenia is a deficiency of platelets (thrombocytes), the cells needed for blood to clot normally. Bleeding beneath the skin or mucous membranes gives rise to small red spots or purple blotches (purpura). The term idiopathic applies when the underlying cause of the disorder is unknown. It is possible that, in ITP, antibodies produced in the spleen destroy the body's own platelets. When an adult with ITP does not respond to medicines such as cortisone-like hormones (corticoids), removing the spleen is effective about two thirds of the time. Doctors often try different drug treatments in the patients who do not get better after spleen removal. A summary of the known effects of the different treatments for these patients might help doctors and their patients make better choices about which drugs to try first.