In a prospective, randomized, controlled trial the effect of high dose intravenous antithrombin III and intraabdominal donor serum was analyzed in 36 patients with diffuse secondary peritonitis. The direct cost for treatment was 25,370 euros per patient, and the post acute hospital care costs and societal costs were 6273 euros. The cost for intensive care of these patients accounted for approximately 83% of the direct costs, while the expenditures for operating theater and general wards accounted for 9% each. The most expensive factors were staff, medication, and blood products. The hospital incurred a deficit of 3696 euros for each patient after reimbursement from public health insurance companies. Quality of life as assessed by the gastrointestinal quality of life index (GIQI) showed a good outcome. On average 11 quality adjusted life years (QALY) were achieved. The cost per QALY was 2631 euros. Use of adjuvant therapy was associated with a reduced duration of intensive care unit (ICU) treatment, times on mechanical respiration, and hemofiltration; the cost of treatment was reduced by 6614 euros per patient. The additional cost of antithrombin III (5155 euros) was more than offset by the savings made when adjuvant therapy was used.