Positron emission tomography (PET) is a noninvasive functional imaging modality that can disclose the presence of a malignant disease. It has recently been reported that PET may be useful to detect primary colorectal cancer (CRC). We present the case of a 47-yr-old man with early colon cancer detected by 18F-fluorodeoxyglucose (FDG) PET. The patient consulted us because of a positive fecal occult blood test and focal FDG uptake in the pelvic cavity detected at a physical check-up. After the usual work up, he was diagnosed as having a sigmoid polyp, 16 mm in diameter. Subsequently, colonoscopic polypectomy was carried out. The surgical specimen was histologically diagnosed as a well-differentiated adenocarcinoma, invading the submucosal layer with lymphatic invasion. Therefore, the involved portion of the sigmoid colon was laparoscopically resected. The FDG PET carried out 1 yr after the operation, showed no abnormal FDG uptake. PET can noninvasively detect an early colon cancer as small as in our patient, as well as other cancers in the whole body. Therefore, we consider it suitable as a screening examination.