The objective of this study was to analyze the genotype distributions and allele frequencies for the Glu298Asp (G894T) polymorphism of the eNOS gene and the serum nitric oxide level among the patients with fibromyalgia syndrome (FS). Ninety-six fibromyalgia patients and 79 unrelated healthy volunteer controls were included in the study. All patients and controls were females. Genomic DNA from 96 patients meeting the American College of Rheumatology 1990 criteria for FS and 79 healthy controls was analyzed by polymerase chain reaction. A polymerase chain reaction-restriction fragment-length polymorphism analysis of eNOS gene polymorphism was performed, and the results of the patients with FS and healthy controls were compared. Ozone-based chemiluminescence assay with Sievers NO Analyzer was used to measure the serum nitric oxide levels. Neither the frequencies of the Glu298Asp genotypes nor the serum nitric oxide levels showed a significant difference between the groups. These results suggested that FS of the Turkish population seemed to develop without any alterations in eNOS Glu298Asp genotype frequency and the serum nitric oxide level.