Subacute thyroiditis is a painful, inflammatory disease of the thyroid gland, probably of viral origin. It is an uncommon but important cause of fever of unknown origin (FUO). We report a case of a 72-year-old man who presented with a 1 month history of fever, headache and weakness, and in whom extensive evaluation only revealed subacute thyroiditis. He was treated with low-dose steroids and became asymptomatic after 2 weeks. In conclusion, when a patient presents with FUO, subacute thyroiditis should be considered as a possible cause even if classic features are absent.