Aim: In this study, we aimed to investigate the prevalence of fibromyalgia syndrome (FMS) in patients with metabolic syndrome (MetS) and its effects on sleep quality and quality of life (QoL).Methods: The study included a total of 84 (56 females, 28 males) patients with MetS, with a mean age of 57.5 (34–74) years and mean body mass index of 32.5 (25–48.9) kg/m2. MetS was defined according to the National Cholesterol Education Program Adult Treatment Panel III criteria. The FMS diagnosis was made based on the 2013 American College of Rheumatology Alternative Criteria. QoL and sleep quality were evaluated by the Short Form 36 (SF-36) and the Pittsburgh Sleep Quality Index, respectively.Results: All patients had diabetes mellitus and were obese or overweight. Of all patients, 73.8% had poor sleep quality and 51.2% had FMS. Patients with both MetS and FMS had a statistically significant female predominance (p<0.001). Impaired sleep was present in 62.9% of patients with both MetS and FMS and 37.1% of patients with MetS only (p<0.001). All SF-36 domain scores were statistically significantly lower in the MetS+FMS group than in the MetS group (p<0.001)Conclusion: The frequency of FMS is high in patients with MetS. Sleep quality and QoL are impaired in the presence of FMS or MetS alone. The co-presence of these conditions causes poorer sleep quality and worse QoL. FMS should be considered in the treatment and followup of patients with MetS.