Splenic pathology was analysed in 73 patients with immune thrombocytopenic purpura who underwent splenectomy for bleeding that had been resistant to adrenocorticosteroids. The mean splenic weight was 100 g. The only notable macroscopic feature was the prominence of Malpighian corpuscles in 15 cases. Microscopic examination showed formation of germinal centres in the lymphoid tissue of the white pulp in 40 cases, prominence of the histiocytes in the red pulp in 18 cases, and infiltration with neutrophils in the same area in 49 cases. Myeloid metaplasia throughout the splenic tissue was minimal in 58 cases, moderate in 15, and extreme in two. No distinguishing features were found in the spleen from patients who had not received previous immunosuppressive treatment (n = 3), those treated with prednisone (1 mg/kg/day) for a median of 14 days (n = 62), or those who had received the same dose of prednisone and additional azathioprine or cyclophosphamide (2 mg/kg/day) for a median of four weeks (n = 8). No correlation could be shown between histological features and the age of the patient or titre of antiplatelet antibodies. Similarly, no distinguishing features were found in patients with associated systemic lupus erythematosus (n = 8), hyperthyroidism (n = 6), immune haemolysis (n = 3), or recent viral illness (n = 3).