A strong infestation of Goniocotes megalocephalus [Mallophaga] on the adult male of Hazelgrouse (Tetrastes bonasia rupestris C. L.Brehm, 1831), which died gradually in cause of a trauma, is described. The result of examination and circumstances of it are dicussed. The poor condition of the bird caused by the trauma and its reduced activity during the winter season were probably the most important factors, on account of these the population of the parasites was increased.