Objective: Anorectal malignant melanoma (ARMM) is a relatively rare form of melanoma, so does knowledge about 18F-fluorodeoxyglucose (FDG) PET/CT of ARMM.We report data suggesting that 18F-FDG PET/CT maybe helpful for diagnosing this uncommon melanoma.Methods: A 57-year-old man diagnosed as anorectal melenoma after the biopsy underwent 18F-FDG PET/CT.We reviewed the features of the whole body PET/CT imaging,including the maximum standardized uptake value (SUVmax), size and location of tumor.Results: Focal increase of FDG uptake in the anal canal of 4cm in length could be detected with SUVmax of 6.1.There was an intensely hypermetabolic liver with a larger size and a decreased density.Lower density nodules within the liver could be identified.The maximum diameter of the nodules was lcm.Intense FDG uptake in the bilateral scapula, ribs, spinal bone and pelvic bone marrow were generally found.No destruction of bone was detected.There was neither abnormal enlargement nor hypermetabolism in systemic lymph nodcs.Conclusions: 18F-FDG PET/CT was not much characteristic for anorectal melanoma but for its strength in detecting metastasis.For patient who is suspious of having melanoma, a range of PET/CT scan should involve from the top of the head to the sole of the foot.