The harbour porpoise is one of the common small cetaceans of European waters. Two large European surveys, SCANS I in 1994 and SCANS II in 2005, indicated a global shift of harbour porpoise distribution in European waters, from northern regions of the North Sea to the southern North Sea, English Channel and Celtic Sea. We have proved that this shift also included the coasts of Brittany in the North West of France using different sources of data, mainly by monitoring the stranding events. As the harbour porpoise is known to be a shelf-water inhabitant often observed in shallow waters, it is likely that conditions offered by the French coasts of the south-west of the western English Channel allow the recovery of a stable population of harbour porpoise in this area. But one feature of our analysis is the almost total absence of stranded calves (less than 5% of all the stranded animals). All these facts raised two major questions concerning the geographical origin(s) of the harbour porpoises stranded around the Brittany coasts for some years, and about their breeding sites. To approach these questions, we have undertaken a genetic analysis of the 29 porpoise samples, collected between 2000 and 2010 on Brittany coasts, contained in the Océanopolis tissue bank. We determined the polymorphisms of 7 microsatellite loci and we are right now sequencing 3 fragments of mitochondrial DNA, often used in population genetic: the 5' part of the COI gene, the coding sequence of the cytochrome b gene and the mitochondrial control region. Twenty-four samples of harbour porpoises stranded in Gironde (south west of France) between 2000 and 2006 were also included in our study. Our results on microsatellite and mitochondrial DNA polymorphisms will be presented, leading to a first hypothesis on the origins of the harbour porpoises stranded in Brittany.