The evaluation of patients with known or suspected recurrent colorectal carcinoma is now an accepted indication for positron emission tomography using (18)F-fluorodeoxyglucose (FDG-PET) imaging. FDG-PET does not replace imaging modalities such as computed tomography (CT) for preoperative anatomic evaluation but is indicated as the initial test for diagnosis and staging of recurrence and for preoperative staging (N and M) of known recurrence that is considered to be resectable. FDG-PET imaging is valuable for the differentiation of posttreatment changes from recurrent tumor, differentiation of benign from malignant lesions (indeterminate lymph nodes, hepatic and pulmonary lesions), and the evaluation of patients with rising tumor markers in the absence of a known source. The addition of FDG-PET to the evaluation of these patients reduces overall treatment costs by accurately identifying patients who will and will not benefit from surgical procedures. Although initial staging at the time of diagnosis is often performed during colectomy, FDG-PET imaging is recommended for a subgroup of patients at high risk (with elevated CEA levels) and normal CT and for whom surgery can be avoided if FDG-PET shows metastases. Screening for recurrence in patients at high risk has also been advocated. FDG-PET imaging seems promising for monitoring patient response to therapy but larger studies are necessary. The diagnostic implications of integrated PET-CT imaging include improved detection of lesions on both the CT and FDG-PET images, better differentiation of physiologic from pathologic foci of metabolism, and better localization of the pathologic foci. This new powerful technology provides more accurate interpretation of both CT and FDG-PET images and therefore more optimal patient care. PET-CT fusion images affect the clinical management by guiding further procedures (biopsy, surgery, radiation therapy), excluding the need for additional procedures, and changing both inter- and intramodality therapy.