Abstract: Objective To explore the causes of fever of unknown origin（fever of unknown origin,FUO）in various regions in recent 10 years and provide reference for clinical diagnosis and treatment of FUO. Methods Retrospectively reviewed the clinical data of 2444 cases of fever in China in the past 10 years. Results Out of 2444 cases, 2195 cases had been diagnosed with a confirmed diagnosis rate of 89.9%. Of the 2195 cases diagnosed, 1,300 cases were infectious diseases, accounting for 53.2%, and 895 cases were non-infectious diseases, accounting for 46.8%. Conclusion The etiology of patients with fever is unclear. Most patients with fever should be diagnosed by reviwing careful medical history, physical examination and laboratory analysis. The main cause of the fever of unknown originis infectious diseases, followed by connective tissue diseases and tumors. For fever patients, apart from routine examination,etiology, imaging, and pathology should be repeated in time for the early diagnosis of the disease.

Key words: Fever of unknown origin, Infectious, Connective tissue, Tumor