Background. Combined fluorine 18-fluorodeoxyglucose-positron emission tomography-CT imaging has been shown to be of good diagnostic value in the preoperative evaluation of patients with colorectal cancer and liver metastases. The adjunctive use of intraoperative sonography (IOUS) may have a limited impact on treatment selection in these patients.Purpose. To compare the diagnostic performance of preoperative positron emission tomography (PET)-CT alone and PET-CT combined with IOUS in the evaluation of patients who are considered for curative resection of hepatic metastases from colorectal carcinoma.Materials and Methods. Patients with colorectal cancer who underwent resection of hepatic metastases and preoperative PET-CT (with or without contrast-enhanced CT) and IOUS were identified. The performance of the imaging techniques was evaluated through review of the radiologic reports, correlation with surgical and histopathologic findings, and clinical follow-up.Results. Thirty-one patients (mean age, 63.5 years [range, 53-82 years]) were analyzed. Fifteen patients had received preoperative chemotherapy. The mean interval between PET-CT and IOUS was 22.6 days (range, 1-56 days). In 4 cases, neither PET-CT nor IOUS correctly diagnosed the liver metastases. In all 31 patients, the sensitivity of PET-CT alone and PET-CT combined with IOUS was 63% (95% CI 44-80%) and 93% (95% CI 78-98%), respectively; the positive predictive value was 81% and 89%, respectively. In patients without preoperative chemotherapy (n 5 16), the sensitivity of PET-CT alone and PET-CT combined with IOUS was 77% (95% CI 49-94%) and 100% (95% CI 79-100%), respectively. In 11 cases (35%), IOUS altered the surgical strategy.Conclusion. In patients with colorectal carcinoma and potentially resectable liver metastases on preoperative PET-CT, IOUS can provide additional information that may alter decision making with regard to surgical technique. Keywords: colorectal cancer; liver metastases; intraoperative sonography; FDG-PET-CT C olorectal cancer is the second leading cause of cancer-related death in the western hemisphere. Up to 70% of patients with colorectal cancer eventually develop liver metastases. In 30-40% of these patients, metastases are confined to the liver at the time of detection. Hepatic resection is the only therapeutic strategy that offers a chance of cure. In patients who undergo successful hepatic resection with curative intent, the expected 5-year survival rate is approximately 33%, and the 5-year disease-free survival rate is 22%. 1 A large number of patients develop intraor extrahepatic tumor recurrence after curative