To reduce operative mortality in elderly patients, a system of preoperative staging, based on invasive monitoring, was developed. All of the 148 consecutive patients studied had been cleared for surgery by standard assessment, but only 13.5% had normal measured, hemodynamic, respiratory, and oxygen transport function. Mild physiologic aberrations, not requiring a delay in surgery, or more severe abnormalities, indicative of high operative risk, were found in 63.5% of the patients. Advanced and incorrigible functional defects found in the remaining 23% made them unacceptable risks for major surgery under general anesthesia, and all who underwent the planned operation in spite of the warning died. Invasive preoperative assessment of elderly patients discloses a high percentage of serious physiologic abnormalities requiring a delay in some and cancellation of the operation in others.