Positron emission tomography (PET) has been successfully used to image colorectal cancer (CRC). This study evaluated the accuracy of 2-[(18)F]-fluoro-2-deoxy- D-glucose (FDG) PET for the detection and staging of recurrent CRC and the consequent impact on clinical management. Forty-two patients previously treated for CRC were investigated for suspected recurrence and, if recurrence was confirmed, the extent of disease was evaluated. All patients underwent whole-body FDG-PET and computed tomography (CT) scan and results were compared to assess sensitivity, specificity and diagnostic accuracy for each modality. We then assessed the FDG-PET directed alteration in clinical management from that planned on the basis of spiral CT results. FDG-PET was more sensitive (93%) than CT (73%) for detection of recurrence (specificity 58% and 75%, respectively). FDG-PET yielded a correct diagnosis in 35 (83%) out of 42 patients, while CT did so in 31 patients (74%). FDG-PET was more accurate than CT for staging local recurrence (sensitivity 100%, specificity 86% with FDG-PET vs 75% and 100%, respectively, with CT) and CRC liver metastases (sensitivity 100% vs 45%; specificity 100% for both). Overall, PET upstaged 8 out of 30 patients (27%) and altered patient management in 16 (38%) cases. This study confirms that FDG-PET is more sensitive than CT for the detection and staging of recurrent CRC. The results also indicate that FDG-PET is an accurate means of selecting appropriate patients for operative treatment. When applied to routine clinical practice, patient management is altered.