Positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) as the tracer of glucose metabolism was performed to identify a postoperative recurrent lesion of rectal cancer. A 66-year-old-man underwent trans-sacral local resection of the rectum for rectal cancer in 1992. A local recurrent mass was discovered, and abdomino-perineal resection of the rectum was performed in 1999. The serum CEA level increased gradually August in 2000, but there was no sign of recurrence on CT or MRI. FDG-PET was performed to reveal a presacral recurrent lesion. Total pelvic evisceration combined with resection of the sacrum, and a bilateral ureterostomy were performed in April 2001. The beneficial role of FDG-PET in the diagnosis of the postoperative local recurrence of rectal cancer is emphasized.