Fever is one of the complications of the disease, whose etiology may remain unrecognized in diagnostic evaluations in some cases. Avicenna, the Iranian scientist, classified fever on the basis of the etiology of the involved organ, timing of fever, and the involved temperaments. According to him, the three types of fever are Dagh fever, phlegmatic fever, and daily fever. Avicenna emphasized on history taking and careful examination of patients and stated that the physician should ask about anything that is related to the events before occurrence of fever. It seems that understanding the ideas proposed in the traditional medicine can be helpful in diagnosis and treatment of the underlying causes of fever.