The purpose of this study was to estimate the incidence and to establish which factors were associated with an increased risk of hemorrhagic complications in an historic cohort of 117 consecutive and unselected patients with chronic idiopathic thrombocytopenic purpura (ITP). Sixty-eight patients (58%) underwent medical treatment and/or splenectomy and 33 (48% of treated) achieved a complete stable remission. At equivalent platelet count the incidence of major hemorrhagic complications was significantly higher in aged (greater than 60 years) than in younger (less than 40 years) patients (10.4% v 0.4%/pt-y, relative risk = 28.9, P less than .01). A previous hemorrhagic event was identified as another major risk factor for hemorrhage (relative risk = 27.5, P less than .0005), while hypertension and underlying disorders had no influence. We conclude that age more than 60 years and a previous history of bleeding are major risk factors for severe hemorrhages in adults with ITP.