Overwhelming surgical stress exceeding a patient's reserve capacity causes a disruption of homeostasis, leading to various postoperative complications. This study was undertaken to develop a new scoring system, "E-PASS", standing for the Estimation of Physiologic Ability and Surgical Stress, that predicts the postsurgical risk by quantification of the patient's reserve and surgical stress. E-PASS comprises the preoperative risk score (PRS), the surgical stress score (SSS), and the comprehensive risk score (CRS) that is determined by both scores. These scores were computed by a multiple regression analysis conducted on 292 consecutive patients who underwent elective common gastrointestinal operations at one hospital between 1992 and 1995 (internal group). The usefulness of the scores was evaluated in 989 consecutive patients who underwent the same surgical procedures during the same period at another hospital (external group). The morbidity and mortality rates increased similarly in both groups as the CRS increased. A marked step-up of both rates was observed at a CRS > 1.0, reaching mortality rates of 20% in the internal subjects and 28.5% in the external subjects. These results suggest that the E-PASS scoring system is reproducible, and that it may be useful for surgical decision making. This system requires no special examinations and can be used in every hospital.