Speleotherapy (ST) is a non-drug method of treatment which uses the microclimate of underground spaces. Such spaces may be represented by karst caves, salt mines, rock-salt and metal mine workings. The specific environment of underground spaces is the main factor affecting the patient's body. Speleoenvironment is formed by the combination of medical and health-improving components. Microfine salt aerosol is the main component of the speleoenvironment. It is based on the light negative ions arising at high levels of air ionization. The other components of the speleoenvironment are the constancy of the microclimate, temperature background, humidity, air flow rate. Another important factors are the absence of allergens and low bacterial contamination. Shielding effect ot the underground space, protecting from the exposure to radio-magnetic radiation is also mentioned. The main stages of the formation and development of the ST method in the world practice are also discussed in the article. Various types of speleological hospitals and the peculiarities of their geographic location are described. The factors of the speleoenvironment are presented. These factors affect the patient's body if the method is used under various conditions.