An analysis of 205 episodes of bleeding encountered during a 7 year period by the staff of a surgical service has been described. Of 168 postoperative bleeding episodes, 80 were associated with anticoagulant or antiaggregant treatment, 51 were caused by technical error, and 37 were associated with sepsis. Of 18 hemorrhages after invasive procedures, 12 were associated with anticoagulants. In the whole series, in 33 of 111 episodes in patients receiving antithrombotic drugs, there was some deviation from standard accepted protocols. Bleeding occurred in the surgical wound or at the site of operation or puncture in 154 instances. Some of the bleeding episodes, especially at other sites, presented in an unusual manner and posed a diagnostic problem. Bleeding was responsible for death or contributed to death in 11 patients, and in 32 patients, it caused operation or reoperation. Other short- and long-term morbidity was also caused. As in many complications, prevention is of the essence.