Among the 1,000 cases of direct surgery on cerebral aneurysms, two cases showed clear signs of preoperative and 19 cases showed postoperative gastrointestinal bleeding. Here we have made a clinical analysis of various aspects of the 19 cases in which the bleeding developed postoperatively. (1) Gastrointestinal bleeding was most frequent postoperatively in cases of VBA aneurysms (4.3%) and AcomA aneurysms (2.9%) and less common in MCA and ACA aneurysm cases. (2) Gastrointestinal bleeding was most frequently seen in those cases operated on between the third and seventh days from the last hemorrhage attack (9.0%) and was more common in those cases with a relatively poor preoperative grade. (3) The development of such bleeding in cases with a good preoperative grade was due to problems with the surgical operation in most cases, although the influence of vasospasm must not be ignored. The development of bleeding in cases with a poor preoperative grade is thought to be due primarily to vasospasm and transitory brain damage to the hypothalamus and the orbital portion of the anterior lobe due to hematoma caused by aneurysm rupture. (4) First the location of gastrointestinal bleeding should be determined endoscopically and, if hemostasis is not possible even after attempted coagulation, then the desirability of surgery should be determined in an early period and abdominal surgery performed.