To identify individual risk factors and to establish an index of risk in biliary tract surgery, data on 16 potential predictive factors were compiled from a series of 186 biliary tract operations excluding simple cholecystectomy. Eight factors had a significant association with postoperative mortality. Linear discriminant analysis showed that serum creatinine, serum albumin and serum bilirubin levels in the week before surgery had independent significance in predicting postoperative mortality. The discriminant function derived identified a high risk group of patients and the predictive value was confirmed in an independent series of 54 biliary tract operations carried out in another surgical unit. The discriminant function derived for patients jaundiced before surgery also defined a high and low risk group and was similarly validated. Identification of high risk patients undergoing surgery for obstructive jaundice may be useful in defining a group of patients to be considered for trials of preliminary biliary drainage.