ObjectiveTo review the current known causes of hyperacusis and the different hypotheses concerning its etiology, and to suggest clinical guidelines.Data SourceA review of the literature with the aid of the MEDLINE database, using the following key words: hyperacusis, intolerance to sound, loudness discomfort level, and phonophobia.Data ExtractionThe data collected included clinical studies, case reports and laboratory studies.ConclusionHyperacusis was shown to be caused by pathologic conditions of the peripheral auditory system, diseases of the central nervous system diseases, and hormonal and infectious diseases. In some cases there was no known cause. The pathophysiology of hyperacusis probably involves a central mechanism rather than a peripheral one. Suggested clinical guidelines and treatment are discussed.