Coenzyme Q(10) (CoQ(10)) is an essential electron carrier in the mitochondrial respiratory chain and a strong antioxidant. Signs associated with skin alteration and mitochondrial dysfunction have been observed in patients with fibromyalgia (FM). The aim of this study was to analyze CoQ(10) levels, mitochondrial dysfunction, and oxidative stress in plasma, blood mononuclear cells, and skin biopsies from FM patients.We studied CoQ(10) level by HPLC in plasma, blood mononuclear cells, and skin obtained from patients with FM and healthy control subjects. Oxidative stress markers and mitochondrial respiratory chain enzyme activities were analysed in both plasma, blood mononuclear cells, and skin biopsies from FM patients.Oxidative stress, mitochondrial dysfunction, and CoQ(10) deficiency have been observed in blood mononuclear cells and skin biopsies.In our patients, mitochondrial dysfunction and CoQ(10) deficiency are present in several tissues. These results may contribute to the understanding of the pathophysiology of FM, and, moreover, CoQ(10) deficiency could represent a good marker for the diagnosis of FM.