We studied 83 patients who had chronic idiopathic thrombocytopenic purpura refractory to steroid therapy and who underwent splenectomy. The positive rates of antiplatelet and antinuclear antibodies were 40% (30/75 patients tested) and 41% (25/61 patients tested), respectively. The morphologic characteristics of splenic pathologic findings included prominent secondary follicles and foamy macrophages, present in 23 (28%) and 56 (67%) of patients, respectively. Extramedullary hematopoiesis was noted in 50 (60%) of the patients. Eight patients (10%) presented with periarterial fibrosis, and three of them had systemic lupus erythematosus. The 23 patients (28%) with prominent secondary follicles were younger than the other patients, were preponderantly female, and had a higher rate of antiplatelet antibody production, and all had an initial response with a greater increase in platelets postoperatively. Eight patients (10%) had neither prominent secondary follicles nor foamy macrophages and lower splenic weights; their initial response compared with that of other patients was significantly poorer. The thrombocytopenia in these patients might have a different mechanism.