Multiple techniques can be used to detect the presence of Hazel Dormice and as a result, there is reasonable confidence that lack of detection means that dormice are probably absent. In the UK, ancient woodlands are frequently considered as the reservoir of Hazel Dormouse populations and are a usual starting point for surveys. However, we present evidence that this may be one of the most difficult habitats in which to detect the species. This is largely due to many of these woodlands being unmanaged, with a poorly developed shrub layer due to heavy shading. This reduces the probability of finding natural field signs such as nests and chewed hazel nuts. Similarly, because detection devices (nest boxes, nest tubes and footprint tunnels) are typically positioned no more than two metres from the ground for ease of study, there is an assumption that Hazel Dormice will leave the dense canopy to use them. We predict that there is a higher risk of false negatives in this habitat type and that more research is needed to provide better certainty of detection when surveying in high canopy woodland.