[Fever of unknown origin in adults].

Fever of unknown origin has been defined as axillary temperature higher than 37.8 degrees C on several occasions, persisting without diagnosis for at least 3 weeks in spite of at least 1 week's investigation in hospital. Lately, the definition has been modified and extended to reflect evolutionary changes in clinical practice. In response to this new evolving environment, cases of fever of unknown origin are currently classified as: classic, nosocomial, in neutropenia, and human immunodeficiency virus-related. The objective of our review was to try and define and to update the information on the subject.