The aim of this study was to evaluate the effectiveness of balneotherapy on patients with fibromyalgia (FM) at the Dead Sea. Forty-eight patients with FM were randomly assigned to a treatment group receiving sulfur baths and a control group. All participants stayed for 10 days at a Dead Sea spa. Physical functioning, FM-related symptoms, and tenderness measurements (point count and dolorimetry) were assessed at four time points: prior to arrival at the Dead Sea, after 10 days of treatment, and 1 and 3 months after leaving the spa. Physical functioning and tenderness moderately improved in both groups. With the exception of tenderness threshold, the improvement was especially notable in the treatment group and it persisted even after 3 months. Relief in the severity of FM-related symptoms (pain, fatigue, stiffness, and anxiety) and reduced frequency of symptoms (headache, sleep problems, and subjective joint swelling) were reported in both groups but lasted longer in the treatment group. In conclusion, treatment of FM at the Dead Sea is effective and safe and may become an additional therapeutic modality in FM. Future studies should address the outcome and possible mechanisms of this treatment in FM patients.