PURPOSE:The aim of this study is to assess the potential role of PET in patients with unexplained rising CEA levels after curative resection of colorectal cancer or for differential diagnosis of the result by conventional radiologic study. METHODS:18 patients with abnormal CEA levels and normal results of conventional methods of tumor detection and 7 patients who needed differential diagnosis after conventional X-ray were studied with PET. The PET results were compared with pathologic findings or conventional radiologic and clinical follow-up for 6 months. RESULTS:PET showed increased uptake in 17 of 25 patients. Using PET in 18 patients with elevated carcinoembryonic antigen levels, 12 patients showed increased uptake of FDG. Among them, 11 positive findings were turned out to be a true recurrence and there was one false positive finding. Six patients with elevated carcinoembryonic antigen levels showed normal PET scan. But conventional X-ray or repetition of PET confirmed the recurrence in 2 patients among them. Using PET in 7 patients for differential diagnosis of conventional X-ray, 3 patients showed hot uptake of FDG and all of them were turned out to be a true recurrence. There were no abnormal findings in 4 patients but one patient among them showed a hepatic recurrence. It was confirmed by abdominal MRI. Overall, sensitivity was 82.4% and specificity was 87.5% CONCLUSIONS:When conventional examinations are normal except CEA elevation or equivocal, PET is a valuable imaging tool for the detection of recurrence.