During the period 1985-1989, 49 patients underwent splenectomy for chronic idiopathic thrombocytopenic purpura in our department. A correct follow-up was available for 39 patients. All patients had been previously treated with corticosteroids. We evaluated the platelet count one year after the operation and the relation between this count and several preoperative and postoperative factors. We observed a favourable prognosis when the preoperative study of platelet sequestration showed splenic destruction, when the duration of symptoms was less than one year and when there was a rapid increase in the platelet count during the first week after the operation.