The discovery of 100 isolated teeth of Sicista betulina Pallas, 1779 in a doline filling of northwestern Switzerland (Vâ Tche Tchâ locality, Courtedoux, Ajoie) represents, in terms of richness, an exceptional occurrence for the Late Pleistocene of western Europe. This reference collection provides additional data for the identification of S. betulina, but also for the distinction of northern Birch Mice (S. betulina) and southern Birch Mice (S. subtilis) populations by morphometrical analyses (Mahlanobis distance, ratio diagrams) from isolated back teeth. Moreover, the determination of these two species is important for palaeoenvironmental studies, because they are associated to different biotopes.