We have analysed the blood transfusion requirements in 288 consecutive adult patients undergoing cardiac surgery using data from the discharge reports, coded in accordance with the international disease classification. 114 patients were transfused (39.6%). The transfusion rate was higher in patients with a principal diagnosis of two valve disorders, acute/subacute ischemic heart disease, congenital anomalies, tumour and injuries. All of these had a transfusion rate greater than 50%. Controlling the confounding effects by multivariate logistic regression analysis, there was an adjusted association of the transfusion rate only with the principal diagnosis and with sex, not with type of admission, preoperative anemia, surgical procedure or age.