Insomnia is one of the most prevalent sleep disorders characterized by sleep difficulty that impairs daily functioning and reduces quality of life. The burden of medical, psychiatric, interpersonal, and societal consequences of insomnia expresses the importance of diagnosing and treatment of insomnia. The aim of study was to investigate causes of insomnia from the viewpoint of Iranian traditional medicine.In this review study, we searched insomnia in a few of the most famous ancient textbooks of Iranian traditional medicine from different centuries. This books includeThe Canon of Medicine by Avicenna (the first version of Beirut), Zakhire Kharazmshahi by Jurjani (the scanned version of Bonyade Farhang-e Iran), Malfaregh by Razes (the first version of Iran University of Medical Sciences), and Aqili's cure by Aqili (the first version of Iran University of Medical Sciences).This study found that in Iranian traditional medicine manuscripts, insomnia was called sahar and even though many factors induce insomnia, most of them act through causing brain dystemperament.The brain dystemperament is considered one of the main causes of insomnia and insomnia can be well managed with an organized line of treatment, by correcting the brain dystemperament through elimination of causes. This study helps to find new solutions to treat insomnia.