Objective To summarize the causes of patients with fever of unknown origin (FUO) and to analyze the relationship between infectious diseases and FUO,in order to provide envidence for experiential therapy.Methods Clinical data of 374 FUO inpatients at He'nan Provincial People's Hospital from June 1,2009 to May 31,2013,including gender,age,diagnosis and department were analyzed retrospectively.Results Three hundred and twenty-seven cases among the overall 374 FUO patients (87.4％) were eventually etiological diagnosed based on supplementary examinations or diagnostic treatment.As for the causes of fever,209 were infection,accounting for 55.9％,among which 78 cases (20.9％) were diagnosed with tuberculosis,23 cases (6.1％) brucellic diseases,19 cases (5.1％) rickettsia infection.Meanwhile,the noninfectious diseases,such as connective tissue diseases (47,12.6％),hematonosis (37,9.9％) as well as the solid tumors (13,3.5％) also constituted considerable shares of the causes for FUO.However,the causes of 47 cases (12.6％) were not identified before discharge.Conclusions Infectious diseases are the main cause of FUO,in which tuberculosis accounts for the majority.Brucellosis and rickettsia infection also account for a considerable proportion.The causes of most FUO cases could be identified through detailed analysis of clinical data and supplemental examinations.