Tan Y, et al. - In order to improve the understanding of fever of unknown origin (FUO), researchers conducted this study to assess the clinical features and outcomes of patients diagnosed with FUO at admission and discharged without final diagnoses after systematic examination in the Department of Infectious Diseases at Peking Union Medical College Hospital between 2004 and 2010 via following them up by telephone. They followed 58 patients with FUO between 2004 and 2010 for a median duration of 518 weeks. Fever duration was 24.6 weeks. In 11 patients, final diagnoses were established, and the diagnostic methods comprised clinical diagnosis, diagnostic therapy, genetic screening and biopsy pathology. In 35 patients, fever subsided during hospitalization or after discharge. Periodic fever was observed in two patients during prolonged observation: one patient required intermittent use of NSAIDs, and the other required intermittent use of NSAIDs and a steroid. Severe and worsening conditions related to the febrile illness led to death in 9 of 10 reported death during follow-up. The investigators, therefore, recommend performing long-term follow-up in patients with undiagnosed FUO.