Patients with fibromyalgia syndrome (FMS) have a nonspecific postural balance disorder and a greater prevalence of falls. Objective: to clarify which aspects of maintaining balance are associated with the impact of the disorder and with balance confidence. Methods: A total of 182 persons with FMS agreed to participate in this study. After re-evaluation, 57 fully met inclusion criteria: age 40–70 years and moderate-severe impact of the illness according to the Fibromyalgia Impact Questionnaire (FIQ). All participants underwent a posture control analysis with a stabilometric platform, an evaluation of the perception of verticality and an exploration of the vestibular system via functional tests. Additionally, they self-completed questionnaires about balance confidence, central sensitization, pain catastrophizing, kinesiophobia, dizziness and days with episodes of instability. Results: The FIQ was associated with central sensitization and dizziness, which explained 56% of its variance (AdjR2 = 0.566), while days with instability, kinesiophobia and dizziness also explained more than half of the variance of the balance confidence scale (AdjR2 = 0.527). A high percentage of positive responses was found for functional tests (>50%) and a high dispersion in the stabilometric parameters. Conclusion: the detection of factors susceptible to intervention, such as disability due to dizziness, takes on special relevance in patients with FMS.