A method for preoperative assessment of surgical risk, in function of several risk factors, was developed using the multiple logistic function, as a model of multivariate statistical analysis. This model has the advantage to express the two considered outcomes (perioperative complications and death) in numerical terms of probability. The data were obtained from 1182 consecutive patients, 14 yrs or more, admitted to six centres in various regions of Italy. Stepwise logistic regression model was applied to a set of preoperative and operative factors, three of which were found to significantly correlate with postoperative hepatic failure: compromission hepatic function time of surgical operation > 120' and nutritional status. The factors significantly correlate with postoperative renal failure were: compromission renal function, bacterial contamination during surgery, time of surgical operation > 120'.