Wild boar, Sus scrofa have been extinct in the wild in Britain for about 300 years. However, escapees from farm enclosures have been noted for over 20 years in parts of Southeast England, and populations of free-living feral boar have now established. Boar root for food on the woodland ground where hazel dormice, Muscardinus avellanarius hibernate in fragile nests and thus may impact on their population through predation. A group of twelve woodland sites assessed as suitable for supporting dormice and where wild populations of boar were known to have been present for ca. 20 years were chosen in Sussex (boar-positive sites). An additional twelve sites without boar presence (boar-negative) were chosen in the same region from the National Dormouse Monitoring Programme (NDMP). Fifty nest boxes were erected in early spring 2009 at each new site and all were inspected in June and October until the end of 2012. The numbers of individual dormice, empty nests found, and nest boxes used by dormice annually were compared between the two groups. The correlative GLM comparisons (using a negative binomial model) for all three indices were significantly higher in the boar-negative sites, suggesting that boar have negatively impacted on, but not eliminated, dormouse populations. Potential confounding variables including soils and woodland classification were investigated and were similar between the groups. Since the study was over a four year period any initial neophobic reaction to new nest boxes on the boar-positive sites would be unlikely to influence the result. We had no data for boar densities so could not evaluate boar versus dormouse density.