The retrospective case-control study explored the possible associations between peri-operative anemia and post-operative mortality status. Cases were defined as those who died within 30 days of the operative procedure and controls as all those who survived. There were approximately eight controls per case. Participating surgeons who operated on Jehovah's Witness patients within the preceeding five years provide a list of patients. Charts of patients were reviewed to determine if any died within 30 days of surgery. If the patient was discharged prior to 30 days postoperatively, then the National Death Index was used to assess the patient's status 30 days after surgery. The incidence of post-operative death, with 95 percent confidence levels, was calculated for strata of pre- and post-operative hemoglobin levels and operative blood loss. The death rate was calculated after stratifying the patients based on status with regard to co-morbid diseases or other possible risk factors.