The dormouse Eliomys quercinus is a forest rodent undergoing long periods of winter hibernation. The species presents a surprisingly large diversity of chromosomal races, which geographic distribution was shown recently to predate the Pleistocene glaciations. Previously reported data on the karyotypes of the garden dormouse in France come from the northeast of the country, where the 2N050 race occurs. New data are presented from specimens trapped near the Atlantic coast (departments of Vendée and Charente-Maritime), in the Pyrenees, the Alps and in the Massif Central. The French Alpine chain, close to the Italian border, is inhabited by the 2N054 race. A karyotype with 2N048 chromosomes, of Iberian type, is found north of the Pyrenees, near the central Atlantic coast and also in the south of the Massif Central, whereas the 2N050 race occurs in the north of the massif. A hybrid between these two races (2N049) was found in Vendée. These facts reveal that neither the Pyrenees nor the Alps constitute a biogeographic barrier to the dormouse and strongly suggest that the present population of northern France derives from a postglacial recolonisation movement initiated in the southernmost regions of France or in the Rhône valley.