Background: Advances in chemotherapy and surgery have increased the number of colorectal cancer patients eligible for hepatic resection. Detection of extrahepatic metastases is important to avoid futile liver surgery. Uncontrolled studies have reported change of management in 20-30% of cases when PET staging is compared with CT alone. There are no large RCTs assessing the additional benefits of PET/CT after the decision to operate based on high quality CT imaging. Methods: A multicenter trial where 404 patients with CAM deemed eligible for hepatic surgery were randomized 2:1 to PET (with a PET/CT) or no PET. Abnormal PET findings were characterized with further imaging +/- biopsy. Surgeons reported planned and actual surgery at specific times in both arms. The primary objective was to determine the proportion of patients who had a change in management resulting from PET defined as cancelled liver surgery (including open/close surgery as a result of PET) and more extensive liver or additional organs surgery. The use of a no-PET control arm ensured a true surgical comparator and will allow a survival analysis in the future. The sample size was based on the assumption that 25% of PET patients would have a management change, and 15% would avoid futile surgery. Results: Between Nov 2005 and Apr 2010, 404 patients were randomized: 270 to PET. Of the 263 patients with PET, 20 (7.6%) had a change in management based on PET; 10 (3.8%) avoided futile laparotomy, 3 (1.1%) had directed open/close procedures (1 laparoscopy, 2 laparotomy), and 7 (2.7%) had more extensive liver (3) or additional resectional organ surgery (4). Liver resection was performed in 93% of PET and 93% of control patients. Open/close surgery occurred in 10 (3.7%) and 4 (3.0%) patients in the PET and control arms respectively. Conclusions: The addition of staging PET/CT in patients with CAM prior to planned liver resection had substantially less impact on surgical management than expected. Our study highlights the importance of comparative effectiveness research to evaluate imaging technology in an era of rising health care costs.