Positron emission tomography (PET) using 18F-fluorodeoxyglucose can sensitively detect cancers of increased glucose metabolism. We describe three asymptomatic individuals who were found to have colorectal cancer and underwent potentially curative surgery. On the PET images, lesions were easily discernible. Our experience and the experience of others suggest that primary colorectal cancer can be detected with PET in a resectable stage. Our three cases are presented and the potential utility of PET is discussed.