Different subtypes of Listeria monocytogenes were isolated from various animal and environmental samples during an episode of increased mortality on a fallow deer (Dama dama) farm. During a 4-wk period, six fallow deer died, including four does, one fawn, and one adult buck. Prior to death, one of the does had exhibited central nervous system signs characteristic of listeriosis. Postmortem examination of the six deer showed no histologic changes typical of listeriosis, although inflammatory changes were present in several organs. Different subtypes of L. monocytogenes were isolated from brain samples from six deer, from fodder and soil from the deer feeding area, and from faces of some healthy animals on the farm. Listeria monocytogenes, which was frequently isolated in the environment of the farm, was considered the probable major cause of mortality in these fallow deer.