This is a retrospective study of older patients admitted to the First and Second Affiliated Hospitals of Wenzhou Medical College, China, with a diagnosis of fever of unknown origin. The study took place from January 1998 to December 2006 among 102 patients who fulfilled the criteria. Infections were responsible for 50 cases (49.1%), followed by no diagnosis in 27 (26.5%), miscellaneous in nine (8.8%), neoplasms in eight (7.8%) and connective tissue disease in another eight (7.8%). Mycobacterium TB was the most frequent type of infection diagnosed.