A 46-year-old man was found to have an increased carcinoembryonic antigen level (25.7 μg/L) during physical examination, and an (18)F-FDG PET/CT scan was subsequently performed. The PET image indicated abnormal radioactivity levels in the left kidney, and the coregistered CT revealed compression of the left renal vein between the aorta and superior mesenteric artery. An ultrasonography was then performed, which revealed that the ratio between the renal hilum and the aortomesenteric left renal vein was 3.2. Therefore, the nutcracker phenomenon was diagnosed. When abnormal radioactivity is found in the left kidney on PET/CT scanning, the nutcracker syndrome should be considered.