['Fibromyalgia (FM) is a chronic pain syndrome of unknown etiology, which affects predominantly women. Among the alterations that have been implicated in the pathophysiology of FM, there have been postulated disturbances in serotonin levels and metabolism, and their implication in symptoms. The aim of the present study was to assess the correlation levels between low levels of serotonin and severity of symptoms in FM.', 'We determined serotonin levels using an ELISA kit in serum from 38 FM patients and 25 healthy individual. Results were correlated with symptoms regarding pain, depression, impact of disease (FIQ) and age.', 'Serotonin levels were decreased by 45% compared to healthy individual. An important correlation was observed between serotonin levels and predetermined parameters of pain, depression, FIQ and age.'] Does [ Low levels of serotonin in serum correlate with severity of fibromyalgia ]?