Objective: Patients with fibromyalgia syndrome (FMS) have mild cognitive dysfunction. Higher serum uric acid (UA) levels in some diseases are reported to be associated with cognitive impairment. Mean platelet volume (MPV) is an indicator of platelet activation. Activated platelets may play a role in neuroinflammation and cognitive dysfunction. The purpose of this study was to compare cognitive functions of FMS patients and controls and investigate the relation of serum UA and MPV levels with cognitive functions. Method: Fifty-four patients with FMS and 33 healthy controls were enrolled,retrospectively. Evaluations were performed with Visual Analog Scale (VAS), Fibromyalgia Impact Questionnaire (FIQ), Beck Depression Inventory(BDI) and to asses phychological status and cognitive impairment Mini Mental State Examination(MMSE) was used in both groups. Results: Mean VAS and sleep quality of FMS group were significantly higher than the control group (p<0.05). Mean MMSE score was statistically significantly lower in the FMS group (p=0.0001). There was not statistically significant correlation between serum UA levels and VAS pain/sleep quality, FIQ, BDI and MMSE scores (p>0.05). No significant correlation was found between serum MPV levels and VAS pain/ sleep quality, FIQ, BDI and MMSE scores (p>0.05) but declined cognitive functions were determined in the FMS group when compared with the control group. Conclusion: Declined cognitive functions were determined in the FMS the FMS group when compared with the control group. Although we did not determine an association of serum uric acid and MPV levels with cognitive functions, larger prospective studies with longer follow up periods are warranted to elucidate the role of these biomarkers in FMS and to determine the factors affecting cognitive functions.