The vegetation composition and the physical-chemical properties of waters were recorded on spring fens in the northwestern Carpathians (the Moravskoslezské Beskydy Mts., the Turzovská vrchovina Mts., the Kysucká vrchovina Mts. and the Bieskid Żywiecki Mts.; Czech Republic, Slovakia, Poland). Combinations of species groups, which indicate mineral ion concentration levels in the water, have been used in delimitation of plant communities. The poor-rich trophic gradient controls the major vegetation gradient. Five widely distributed communities were distinguished along this gradient: the Valeriano-Caricetum flavae association (rich alkaline spring fens depositing peat, moderate slopes), the Sphagno warnstorfii-Eriophoretum latifoliae ass. (moderately rich, neutral spring fens or alkaline sources of poor water or advanced succession stages), the Caricetum goodenowii ass. (moderately poor, neutral sites with low organic content in the soil), the Carici echinatae-Sphagnetum sphagnetosum flexuosi subass. (poor spring fens with a stable water regime and moderately acid pH) and the Carici echinatae-Sphagnetum sphagnetosum fallacis subass. (strongly acid poor fens, especially sites with lowered water table). Two other rich fen communities, the Eleocharitetum pauciflorae and the Carici flavae-Cratoneuretum, were found only occasionally in the study area. The vegetation composition correlates best with the pH and conductivity of the water. Both the water redox-potential and the altitude also increase towards the poor end of the gradient. There is an important group of subatlantic species occurring in the study area, generally rare in the Western Carpathians. These species grow mainly in the central part of the major vegetation gradient, on moderately acid and moderately poor fens (Caricetum goodenowii, Carici echinatae-Sphagnetum sphagnetosum flexuosi).