Squamous cell carcinoma (SCC) of the rectum is extremely rare with a reported incidence of only 0.025-0.1% of all colorectal tumors. The patient was a 68-year-old man who presented with fatigue, dry cough, shortness of breath, and unintentional weight loss. A chest CT revealed a left suprahilar mass suspected to be lung cancer and an initial diagnosis of primary lung cancer was made. However, fluorodeoxyglucose positron emission tomography and computed tomography (FDG-PET/CT) exam revealed an intensely hypermetabolic rectal mass which turned out to be rectal squamous cell carcinoma. This is the first report that shows FDG-PET/CT images of rectal squamous cell carcinoma metastasis to the skin, muscle, bone, and lung. Use of PET/CT in the initial diagnosis of non-resectable rectal cancers may avoid unnecessary surgery.