Purpose: The aim of this study was to evaluate the efficacy of FDG-CDET for the detection of recurrences of colorectal cancer, in occult disease or in doubtful cases at conventional imaging (CI). In all the evaluated cases, the result of FDG-CDET was compared with post surgical histology both on patient and on site bases.Methods and patients: After fasting for 6h or more, 150-250 MBq of 18F-FDG were injected i.v. and 2D imaging (whole-body scan and at least a tomoscintigram) was started 45 min. later, using a PICKER CDET gamma camera. Among the 214 examinations (ex) performed for detection of recurrences of colorectal cancer between Jul 1997 and Feb 2000, we only considered the 58 cases with negative or questionable CI and a post surgical histologic proof.Results: Patients were referred in three different contexts: