During the last two decades, populations of the wild boar Sus scrofa in Europe have increased considerably and the species has spread into new areas over the entire continent. Because of the animals' impact on agriculture, livestock and biodiversity, and the resulting necessity of realistic management practices, we were interested in the key environmental factors responsible for this remarkable development. The study was based on data from the canton Thurgau, a region in north-eastern Switzerland. We used data on damage and hunting success to calculate a population density index and related it to eight variables describing ecological conditions, demography and hunting pressure (measured by the number of hunters) over a 25-year period. The analysis shows that the population increase correlates with higher than average winter and spring temperatures and improved food supply through more mast years and an increase in the area of maize cultivation. While favourable temperature conditions mainly reduce juvenile mortality, enhanced food availability is likely to boost reproductive success through younger age at first reproduction, larger litter size and earlier onset of oestrus within a season. Given this link between food and reproduction, supplemental feeding, a management practice recommended and very common all over Europe, should be reconsidered.