Fever of unknown origin (FUO) has been rarely associated with colonic cancer. In less than 1% of cases of FUO a colonic cancer is found as the main cause of fever. The authors reviewed 4 cases of colonic cancer whose first manifestation was FUO. Recurrent episodes of brief, self-limited fever, without a characteristic pattern, may be the first symptom of colonic cancer. On occassions, E. coli bacteremia may be the herald of an occult colonic malignancy.