We performed an economic analysis of the care provided to patients undergoing major abdominal surgical procedures to determine the effect of postoperative infection on hospital resource use. Patients' clinical and demographic characteristics and their use of medical care services were determined from a review of hospital bills and medical records. Hospital charges were obtained from the hospital billing system and costs were determined by use of Medicare cost-charge ratios obtained from the hospital's Medicare Cost Report. The care of patients with postoperative infections was significantly more expensive than that of uninfected patients (multivariate analysis indicated that a surgical infection added $12,542 to the cost of patient care). Patients with postoperative fever but without documented infection were also more expensive to care for than afebrile, uninfected patients (fever added $9145 to the cost of care). Increased costs for infected patients were found among microbiology tests, radiology services, pharmaceutical costs, and room costs. For these patients, we found that use of departmental cost-charge ratios, instead of hospital-wide cost-charge ratios, had no substantial impact on comparison of the cost of care for infected and uninfected patients.