ABSTRACT: Hydrogeochemical conditions in Neogene volcanic complexes are very specific and variable. Besides the determining mineralogical – petrographic composition of the neovolcanic rocks and their structural properties, a series of factors form the groundwater chemical composition. This consists of groundwater temperature, pressure conditions, concentration and partial pressure of CO2, oxidation-reduction conditions, ground-water flow velocity and circulation depth. In some places, the final chemical composition of ground-water is influenced by anthropogenic factors such as industry, agriculture, tourism, and mining activities. These factors vary in intensity and pollution of the atmosphere and infiltration of precipitation waters has already occurred. Research focused on evaluation of the chemical composition of ground-water from neovolcanic rocks in Slovakia was performed by the Department of Hydrogeology between 2004 and 2006. This evaluation was undertaken by statistical assessment of 1 921 ground-water analyses of the neovolcanic rock environment used for compilation of the Slovak Geochemical atlas. Groundwater in the Eastern neovolcanic provinces of Slovakia (The Slanské vrchy and Vihorlat Mts.) and in the Central and Southern ones (Pohronský Inovec, Vtáčnik, Kremnické vrchy, Štiavnické vrchy, Javorie, Krupinská planina and Cerová vrchovina Mts.) was studied separately, and then compared and classified using Gazda´s classification.