Whole-body positron emission tomography (WB PET) was performed preoperatively in 24 patients with primary colorectal cancer, and the results were compared with the histopathological findings. The PET positive rate was 95.8% (23/24 patients) for the primary tumor. Among nine patients with histologically confirmed lymph node metastasis, two (22.2%) were positive by PET, including one with n1 and one with n4 disease. Among 15 patients without lymph node metastasis histopathologically (n0), two (13.3%) showed false-positive nodes on PET, being diagnosed as n1 and n3 disease, respectively. These results suggest that preoperative PET is useful for the diagnosis of primary colorectal cancer, but it is of limited value for detecting metastasis to the regional lymph nodes surrounding the primary lesion.