Fibromyalgia syndrome (FS) is associated with a neuroendocrinal disorder characterized by abnormal function of the hypothalamic-pituitary-adrenal (HPA) axis, including hyperactive adrenocorticotropic hormone (ACTH) release and adrenal hyporesponsiveness. Catechol-O-methyltransferase (COMT) enzyme inactivates catecholamines and catecholamine-containing drugs. Polymorphism in the gene encodes for the COMT enzyme. For this study, the significance of COMT polymorphism was assessed in FS. There were three polymorphisms of the COMT gene: LL, LH, and HH. The analysis of COMT polymorphism was performed using polymerase chain reaction (PCR). Sixty-one patients with FS and 61 healthy volunteers were included in the study. Although no significant difference was found between LL and LH separately, the LL and LH genotypes together were more highly represented in patients than controls ( P=0.024). In addition, HH genotypes in patients were significantly lower than in the control groups ( P=0.04). There was no significant difference between COMT polymorphism and psychiatric status of the patients as assessed by several psychiatric tests ( P>0.05). In conclusion, COMT polymorphism is of potential pharmacological importance regarding individual differences in the metabolism of catechol drugs and may also be involved in the pathogenesis and treatment of FS through adrenergic mechanisms as well as genetic predisposition to FS.