Determining the underlying cause of a fever can be a daunting task. Multiple reasons have been found for a patient to have a fever, but the use of an organized approach will assist clinicians in reaching a correct diagnosis. The first step in this process is a complete assessment, including a thorough physical assessment and an evaluation of the history of present illness as well as a detailed review of all the patient's medications. Infection should always be a primary consideration for the cause of a fever. Evaluating each body system can match symptoms with a possible cause for fever, and proper testing and imaging can be pursued. Noninfectious causes of fever need to be included in the differential diagnostic process. This article provides an analytic approach to fever in adult patients in the acute and critical care environment.