Of 38 adult patients with idiopathic thrombocytopenic purpura followed an average of more than 12 years, 15 suffered splenectomy failure or postsplenectomy recurrence of thrombocytopenia. Nine of the 15 also received immunosuppressive agents, and four of the nine failed such therapy. In eight of these 15 treatment failures normal or safe platelet counts were achieved in a subsequent three to 12 year period during which they received no therapy. The frequency of spontaneous recovery of satisfactory platelet levels in adults with idiopathic thrombocytopenic purpura in whom treatment failed may have negative implications for very vigorous or longstanding immunosuppressive therapeutic attempts in certain cases.