The European oyster (Ostrea edulis) was introduced to the Nova Scotia aquaculture industry 30 years ago using stocks imported from naturalized populations in Maine whose ancestors originated in the Netherlands. This study used 5 microsatellites to assess the level of genetic diversity in several hatchery stocks and naturalized populations from Nova Scotia, New Brunswick, British Columbia and Maine. Some genetic erosion was shown to have occurred in the Maritimes populations, with the largest loss of alleles being experienced by the hatchery stocks. In spite of this loss, genetic diversity and heterozygosity in the Maritimes populations are still relatively high. Relationships within and between the populations and the existence of kin groups within the collections were overall consistent with our knowledge of the historical transfers of oysters between different locations. Furthermore, the established database allowed to assign with good confidence unknown oyster samples to their geographic origin. This would be a useful forensics tool in the case of an illegal transfer from a diseased area.