On the occasion of the 170th anniversary of the Société Médico-Psychologique, we review the oldest and most consistently used therapy in medicine: hydrotherapy. It has been practiced for therapeutic purposes since Hippocrates, in the 5th century BC, and has been in existence since then. We should point out that William Cullen, in the 18th century, was the inventor of the neologism of neurosis. He was also a great prescriber of hydrotherapy for these pathologies. Later, the interest of balneotherapy was defended in Austria by Winternitz, then in Moravia by Priessnitz, and in Germany by the famous Kraepelin, Alzheimer, Sioli, and Klemperer, all regular advocates of this therapy, notably for agitated and psychotic patients. There was also a strong faction in the United States, with Professors Draper and Baruch, at Columbia University (New York), or in the American West with Winslow as well as the psychiatrists of the Agnews school who were also convinced prescribers. In France, the development of hydrotherapy was ensured by Esquirol (Salpêtrière and Ivry) and Fleury at the Meudon nursing home. The first writings on balneotherapy showed the interest of using this technique as a treatment for psychotic states and states of agitation, in the form of lengthy cold water baths. This was the case until 1950, when thermal medicine was organized around an institutional medicine using hydrotherapy in a structured way and supervised by a medical-psychological support staff. It was at this time that Dubois and Vidart described what would be called “an institutional therapy of the treatment of psychoneurotic states”. The Société Médico-Psychologique regularly reported on this therapy, which was initially devoted to asylums for agitated and psychotic patients. But with the rise of thermal medicine, this approach was developed in France in centers specializing in mental health. It should be noted that the indications have clearly changed and have been modified with an increasing interest in anxiety disorders, overwork and burn-out, and even certain addictions to benzodiazepines. Some evidence has been provided through scientific studies, supervised by academics, which has allowed hydrotherapy to gain a better defined role in the care of the anxious patient. The main pathologies for which it is effective are: anxiety, burn-out, exhaustion, the aftermath of psycho-trauma, and over-medication. Thereafter, thermal medicine developed through studies demonstrating its effectiveness, which allowed for the establishment of the French Association of Research in Thermal Medicine, but also in the form of a pedagogical approach that was developed by the college of teachers of the SFMTh and adopted.in several French universities. The hydrotherapy approach also developed in the Thermal School of Stress (the thermal baths of Saujon, the pre-eminent hydrotherapy center for mental health) and with the development of programs of care for benzodiazepine withdrawal, 50% of which is covered by the National Health Insurance Fund. In this article, we highlight the place of thermal medicine in psychiatry and mental health and its potential for further development and for providing answers for situations of increasing malaise for which there is a strong possibility of recidivism because of the absence of intrinsic psychiatric pathologies at the origin of these states of decompensation.