The local mineral springs were mentioned as early as 1244. Therapeutic activities started in 1657. In recent past this spa was among the most sought after in the Kingdom of Hungary. Sliač owes its present appearance to the 1930s.
Reputation of this spa has been also increasing thanks to visits of some important figures of public or artistic spheres such as the Hungarian revolutionary Lajos Kossuth, the Czech lady-novelist Božena Němcová, the former Czechoslovak President T. G. Masaryk, the famous Russian politician N. Chruščov, and many other.
Since the 1960s, Sliač Spa has been the only spa in Slovakia that treats cardiovascular diseases, because its exceptional mineral waters can be used in carbon therapy. The waters of the Sliač Spa are unique due to their high CO2 content (more than 98%) and rare isothermal temperature of 33.2°C. They can also be used to treat musculoskeletal disorders, as well as gynaecological and oncological diseases. Sliač Spa is the only spa in Slovakia that uses natural gas for treatments. The gas is acquired directly at the spa’s spring. All other spas in Slovakia make use of chemically-produced gas. The guests at Sliač Spa can choose from more than 45 treatments, including balneotherapy, hydrotherapy, thermal therapy, physiotherapy, and electrotherapy. Some of the more unique treatments include: water carbon dioxide baths, gas carbon baths, and gas injections.