Objective: To develop and validate a tool for evaluating balance and neuromotor function in patients with fibromyalgia (FMS). Methods: Brainstorming, the nominal group technique, and pilot-testing were used to select a battery of 20 functional balance tests that were included in a screening tool. A total of 108 subjects (62 with fibromyalgia syndrome, 22 aged over 65 years, and 24 healthy subjects) participated in this validation study. Factor validity, internal consistency, the ability to discriminate between patients and healthy subjects, and concurrent validity with the Fibromyalgia Impact Questionnaire (FIQ), the Central Sensitization Inventory (CSI), the 12-Item Short-Form Health Survey (SF-12), and other tools for measuring balance, such as the Dizziness Handicap Inventory (DHI), the Activities-Specific Balance Confidence Scale (ABC-16), the Falls Efficacy Scale-International (FES-I), and posturographic parameters, were evaluated. Results: The factorial analysis extracted four factors that explained 70% of the variance. The Alpha Cronbach value was 0.928. Concurrent validity of the screening tool with respect to other tools was high, and the receiver operating characteristic (ROC) curve analysis showed an AUC value of 0.932 for discriminating between healthy and FMS subjects. Severe balance disorder related to head movements in FMS patients was found. Conclusion: The 20-item JAEN (Joint Assessment of Equilibrium and Neuro-motor Function) screening tool is a valid and reliable tool for assessing balance in patients with FMS.