One hundred six patients treated consecutively with total knee arthroplasty were evaluated to determine whether preoperative comorbidity (as measured by patient class, knee score, short form, anesthesia severity assessment, and number of medical comorbidities) correlated with perioperative and postoperative outcomes, including length of stay, total (and specific) hospital charges, and validated outcome scores. The length of stay for total knee arthroplasty was longer in patients who had lower preoperative knee scores and for patients with greater medical and musculoskeletal morbidity. Greater total hospital costs were associated with Class C patients and patients with poor anesthesia morbidity ratings. Patients who were debilitated medically and had four or more risk factors had decreased postoperative outcome scores. Preoperative medical and musculoskeletal morbidity influence the results of total knee arthroplasty. These findings may be useful to surgeons for optimizing resource utilization and outcomes in patients undergoing total knee arthroplasty. These data must be accounted for when contrasting total knee arthroplasty results between different surgeons and institutions.