Lyme neuroborreliosis is the most severe clinical manifestation of Lyme borreliosis. In most of Denmark, and also Europe, the overall prevalence of Lyme borreliosis seems to be stabilising. This is not the case on the island of Funen, Denmark, where the number of human Lyme neuroborreliosis cases has markedly declined throughout the last decade. We propose the reason for the decline is a major epidemic among roe deer, killing almost half of their population, resulting in a reduction in the tick population which make it less likely to get a tick bite and therefore to contract Lyme neuroborreliosis. This is the first time such a relationship is described as a naturally occurring phenomenon in Europe.