The hazel dormouse (Muscardinus avellanarius ) has recently been discovered in County Kildare, Ireland and is being treated as non-native and, hence, potentially invasive. The mode of arrival and origins are unknown; however, initial theories included transfer via hay from Great Britain. The population in Kildare appears to be thriving, and as native populations throughout England are in decline the success is of broad conservation relevance. To gain insight into the recent demography of the County Kildare population, the cytochrome b gene was profiled for individuals from Kildare, England and Wales and compared to known haplotypes throughout its European range. The individuals from County Kildare shared the same previously unrecorded haplotype, which was placed in a separate clade from the GB haplotype, along with more southern European populations. The French haplotype was the most recent closest relative, albeit with a 3 base pair difference, inferring that either the dormouse has been present in Ireland for longer than expected, or it is recently derived from a source population yet to be sampled. The latter is considered the most likely scenario. Future work and concerns about the hazel dormouse in Ireland are discussed.