Objective: Many physiological and pathological processes, such as infections, environmental toxins, and ionizing radiation increase bodily concentrations of oxidizing substances, known as free radicals, which lead to neurodegenerative disorders. Sleep is one of the most important factors contributing to health; however, insomnia is among the most prevalent health complaints. Methods: In this study, for the first time in the literature, we investigated the effects of primary insomnia on certain oxidative stress biomarkers. For this purpose, glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and myeloperoxidase (MPO) activities and levels of reduced glutathione (GSH) and malondialdehyde (MDA) were measured in 30 patients with primary insomnia and 30 healthy volunteers. Results: Our results show that the patients with primary insomnia had significantly lower GSH-Px activity and higher MDA levels compared with the controls. Conclusion: These results may indicate the important role of sleep in attenuating oxidative stress. © 2012 Elsevier Inc.