BACKGROUND: Accurate detection of recurrent colorectal carcinoma remains s clinical challenge. Positron emission tomography (PET) using 18F- fluorodeoxyglucose (18FDG) is an imaging technique that allows direct evaluation of cellular metabolism. 18F-fluorodeoxyglucose PET was compared to computed tomography (CT) and CT portography for staging metastatic colorectal carcinoma. PATIENTS AND METHODS: Twenty-four patients previously treated for colorectal carcinoma who had suspected recurrence to the liver underwent an 18FDG PET scan of the entire body. All patients had either a CT scan of the abdomen (n = 17), a CT portogram (n = 18), or both (n = 11). The final diagnosis was obtained by tissue pathology in 19 patients and clinical follow-up in 5 patients. RESULTS: A total of 60 suspicious lesions were identified. Of the 55 intrahepatic lesions, 39 were malignant and 16 were benign. Of the 5 extra hepatic lesions, 4 were malignant. The 18FDG PET imaging had a higher accuracy (93%) than CT and CT portography (both 76%) in detecting metastatic disease to the liver, and detected unsuspected extrahepatic recurrence in 4 patients. Although the sensitivity of 18FDG PET (90%) was slightly lower then that of CT portography (97%), the specificity was much higher (100% versus 9%), including postsurgical sites. 18FDG PET altered surgical plans in 6 (25%) of 24 patients. CONCLUSIONS: 18FDG PET is extremely useful in staging patients with suspected metastatic colorectal carcinoma to the liver.