A prospective trial was conducted in 386 critically ill surgical patients, the APACHE II score was used to quantify the severity of illness and to judge the outcome. Admission APACHE II score of these patients averaged 15.6 +/- 5.4, the mortality rates rose from 1.9% to 100% when the APACHE II score increased from 0 to 38. The score was closely correlated with the subsequent risk of hospital death for these patients (r = 0.75 P < 0.001). Critically ill surgical patients would be well served by APACHE II for quality assurance or outcome.