The density, patterns of habitat use and diet of sympatric populations of both native red deer (Cervus elaphus Linnaeus 1758) and introduced Japanese sika deer (Cervus nippon nippon Temminck 1836) in southwest Ireland are described. Habitat and dietary overlap between the two species was substantial and the potential for exploitative competition was investigated. Habitat associations and dietary preferences of both species are poorly known. There are also no published estimates of red and sika densities in this area.