BACKGROUND: Although blood is very important therapeutic agent in bleeding patients, it may transmit disease, cause an adverse reaction in the recipients, raise the cost of patient care. Since the misuse and inappropriate use of blood is common, we are to review the transfusion practice in our hospital and to reduce unnecessary blood transfusion. METHODS: During a 10-month period from June 1994 through March 1995, 347 patients received blood transfusion during the operation. Among them, we reviewed retrospectively the charts of 211 patients available. We analyzed the transfusion pattern of 47 patients whose postoperative hematocrit exceeded 32 percent to determine the magnitude and cause of unnecessary blood transfusion. RESULTS: The patients of postoperative hematocrit over 32 percent were 119 patients out of 211 patients(56.4%). The main cause of overtransfusion was no reevaluation of the patients hematocrit after the prior unit was given. CONCLUSIONS: Guidelines for transfusing patients must be constructed based on acceptable intraoperative hematocrits. Unnecessary transfusion can be decreased when the transfusion done according to the guidelines, insisting on each reevaluation of the hematocrit prior to the administration of unit of blood.