The authors applied a mathematical model of evaluation of operative risk to a group of patients undergoing general and obstetric-gynecologic surgery. They verified that all risk factors identified by this mathematical model really influenced operative morbidity and mortality in the present study too. In this univariate analysis, anesthetic technique was found to influence patients' outcome, so it must be included in multivariate analysis protocols. Therefore, this mathematical model showed to be of value in assessing operative risk factors.