The hazel dormouse Muscardinus avellanarius is commonly considered a typical lowland species,though occasional observations have also been reported at higher altitudes in mountains. In this work, we checked the presence of this species at its altitudinal limits in the Alps. Summer nests were searched along two valley floors at progressively higher altitudes. Fifteen nests were found, 10 in Valsavarenche and 5 in Val di Rhêmes, from 1600 m up to the upper tree line at 2032 m, which represents the current altitudinal record for the species. All the nests were composed by layers of different plant matter. This structure may promote insulation and protection from wind and low temperatures, and is typical of reproductive females. Nests were also found in sites surrounded by few woody species, which hardly cover the food requirements of the dormice throughout their season of activity, suggesting the use of alternative resources such as insects or other invertebrates. The presence of hazel dormice at these altitudes indicates that this species can adapt to less diverse habitats and extreme climatic conditions.