Background: The aim of this study was a systematic review of the literature related to adult fever of unknown origin (FUO) in Turkey. Material/Methods: To find the published series, three national and two international databases were searched. Results: Data for 857 patients with the diagnosis of fever of unknown origin were obtained from 13 articles. FUO was defined as fever over 38.3 degrees C that continues at least for three weeks with no diagnosis reached after one week of inpatient investigation in all series (Petersdorf and Beason criteria). Infections, collagen vascular diseases, and neoplasms were found to be the reason of fever in 403 (47.0%), 137 (15.9%), and 126 (14.7%) of the in all 857 patients. The most common infectious disease was tuberculosis (147/403, 36.4%) followed by brucellosis (51/403, 12.6%) and infective endocarditis (39/403, 9.6%). The most common collagen vascular disease was adult-onset Still's Disease (49/137, 35.7%), followed by systemic lupus erythematosus (23/137, 16.7%). The most common neoplasms were Hodgkin's disease (32/126, 25.3%) and non-Hodgkin's lymphoma (32/126, 25.3%). The reason of fever could not be defined in 138/857 (16.1%) patients. Conclusions: Tuberculosis and brucellosis remain common causes of FUO in Turkey. In addition, lymphomas and adult-onset Still's disease should be considered in the differential diagnosis of a patient admitted with FUO.

Keywords: Body Temperature, Brucellosis - diagnosis, Communicable Diseases - diagnosis, Diagnosis, Differential, Fever of Unknown Origin - etiology, Neoplasms - diagnosis, Still's Disease, Adult-Onset - diagnosis, Tuberculosis - diagnosis, Turkey