The degree of maturity of the high mountain forest and the associated malacological fauna.-The influence of forest maturity on the composition of the molluscan community was evaluated. The sampling áreas are situated in Aigüestortes and Estany de Sant Maurici National Park, in the northeast of Spain. According to the results, in the most mature forests the richness of species and the density of populations are less than in the disturbed áreas. Altitude and other environmental factors could also be responsible for this trend.