Mountain butterfly species are often restricted in their distribution and under threat from habitat destruction and climate change. Due to the inaccessibility of their habitats the distributions of many such species are unknown. We have investigated whether information on the habitat requirements of the Alpine endemic species Erebia calcaria could be used for modelling its potential distribution. We surveyed part of its range using transects and recorded habitat and environmental parameters. The most important parameters determining the presence of the species were average height of the vegetation, maximum height of the vegetation, percentage area of bare ground, number of food plants and slope. Furthermore, the abundance of E. calcaria is strongly affected by site exposure and grazing intensity. Using these results we modelled the potential distribution of the species in its known historical range in Slovenia. In the region covered by the model 70% of the records of E. calcaria were within the predicted distribution. It is reasonable to propose that such a high detection rate justifies the use of distribution models for predicting a species range and providing important additional information for their conservation. In the case of E. calcaria, we have shown that endemic mountain butterflies can be strongly threatened by fragmentation of their habitat, overgrazing and succession, which could be further amplified by changes in climate.