Metastasis of rectal adenocarcinoma develops by lymphatic or hematogenous spread. The usual sites of metastasis from rectal adenocarcinoma include local and distant lymph nodes, the liver and the lungs. The current case report presents a unique case of a mass that was identified in the tonsil by positron emission tomography-computed tomography (PET-CT), indicating a metastasis from rectal adenocarcinoma. Metastatic tumor to the tonsil is extremely rare and to the best of our knowledge, no previous studies have reported a case of tonsil metastasis from rectal adenocarcinoma. PET-CT scanners represent an important evolution in technology that is helping to bring anatomical imaging togeother with functional imaging in cancer diagnosis and therapy. Written informed consent was obtained from the patient.