Patients with colon cancer rarely present with pyrexia of unknown origin (PUO) without other manifestations or symptoms. The present paper reports a patient who presented with a 6-month history of fever. The patient was found to suffer from well-differentiated adenocarcinoma of the sigmoid colon. A few days after sigmoidectomy the fever subsided and the patient recovered. Investigation of the large bowel should always form part of the evaluation in patients with pyrexia of unknown origin.