The layout of this study, designed as a randomized crossover clinical trial, is to evaluate the efficacy of an intervention with mineral-medicinal water from As Burgas (Ourense) in patients suffering from fibromyalgia. Pre-intervention: randomization of group A and group B. Intervention: Phase 1: Group A: 14 baths in thermal water for a month and standard pharmacological treatment; group B, standard pharmacological treatment. Rest period, 3 months. Phase 2: Gruop A, standard treatment and Grou B, 14 baths in thermal water for a month plus standard treatment. The Fibromyalgia Impact Questionnaire (FIQ) was used; this grades from 1 (minimum) to 10 (maximum) the impact of the illness, which was measured in both phases. 25 patients were included in each group and the study was concluded with 20 patients in group A and 20 in group B. The intervention group obtained, once the baths finished, a mean score of 60,3 (±11,8) and the control group of 70,8 (±13,0) (p <0,001). Three months later, the intervention group presented a mean score of 64,4 (±10,6) and the control group of 5,0 (±11,3) (p <0,001). We can therefore conclude that the simple baths with mineral-medicinal water from As Burgas can make an improvement on the impact caused by fibromyalgia.