A prospective study was performed to determine the impact of preoperative assessment of estimated postoperative liver volume on surgical decision making for liver metastases from colorectal cancer. Assessment of estimated postoperative liver volume was performed before surgery in 25 patients. Mean estimated postoperative liver volume +/- standard deviation (SD) was 697 cm3 +/- 317 (range, 320-1,532 cm3). Mean relative estimated postoperative liver volume +/- SD was 51% +/- 16 (range, 20%-90%). In two patients, relative estimated postoperative liver volumes of less than 35% prevented resection. These two patients underwent preoperative portal vein embolization, which resulted in marked hypertrophy of the unembolized healthy part of the liver and subsequent safe resection. Before surgery, all patients had a relative estimated postoperative liver volume of greater than 35%, and no cases of postoperative liver failure occurred. The results demonstrated that assessment of estimated postoperative liver volume provides vital preoperative data for reducing the risk of postoperative liver failure.