The consequences of tourist growth on extensive livestock farming were studied in a valley in the Spanish Central Pyrenees (Upper Esera), characterized by important growth in tourist activity during the last 3 decades. The municipalities with the greatest tourist development experienced the biggest drop in livestock farming (abandonment of cultivated land, decrease in livestock population and farms) because of the competition of tourism for labor and fertile land, which are essential to the maintenance of extensive livestock farming. Low use of pasture resources leads to their progressive loss, owing to the advance of plant succession (substitution of pastures by shrubs), decreasing landscape diversity, and increased fire hazard and soil erosion. We conclude that the current model of tourist development in the Spanish Pyrenees represents serious problems in terms of sustainable development.