In order to select those patients with colorectal liver metastases who may have benefit from an operation, preoperative detection and localization of tumors in the liver is necessary. In this study, the specificity and sensitivity of a CT arterial portography and magnetic resonance imaging with contrast media was compared with the results of operative findings and intraoperative ultrasonography. The combination of both preoperative methods led to an accuracy rate of more than 90%, and all patients who underwent laparotomy were resected or treated with an arterial infusion port system. Negative laparotomies were excluded completely.