Overweight, obesity and the metabolic syndrome are usual conditions treated in french balneotherapy care facilities. 42,507 patients were treated last year in France for metabolic conditions, most of them benefiting a social security reimbursed treatment. The therapeutic intervention core is made of hydro-thermal cares: drinking mineral water (alkaline sodium bicarbonated water), individual mineral water bathing, showers, massages under mineral water, mineral water pool collective exercise; education on nutritional concepts, adapted physical activity are also essential informations delivered in group or customized sessions. AFRETH promoted two clinical studies investigating the topic.   The randomised controlled trial Maathermes (1) assessed the benefit of the intervention on 257 overweight or obese patients randomized between balneotherapy (delivered in Brides, Capvern, Vals, Vichy, Vittel) and a control group (usual care and booklet on nutrition from the french health autorithy). At month 14th, the patients treated in the balneotherapy group showed a significant weight reduction (5.17 kg vs .54 kg ; p<.001) and they had more perspective to reach a stable weight loss of 5% (57.1% vs 18.6 % ; p<.001).   Prisme (2), a feasability cohort study, investigated the results of the intervention in 93 patients with a metabolic syndrome treated in Eugenie les Bains. At month 12th, 67 patients could be assessed. Metabolic syndrome had disappeared in 76% of the patients (glycemia normalised in 15%, waist circumference returned to acceptable in 15%, lipidic disorders disappeared in 33% ; blood pressure had acceptable values, without increased drug intake, in 67%.). 75 % of the patients were continuing the adapted physical activity, 65 % had a correct lipid intake.   Balneotherapy is useful for patients with overweight or obesity. Education during the stay is helpful for the weight and metabolic syndrome control. The medico-economic benefit of such an intervention remains to be established on scientific basis.