A survey of naso-pharyngeal myiasis affecting red deer (Cervus elaphus) in southern Spain was conducted. The parasites involved were the larvae of Pharyngomyia picta and Cephenemyia auribarbis (Diptera:Oestridae), which coexist sympatrically within this host. Males and older animals had higher prevalences and intensities of fly larvae. Differences in behaviour and habitat use by male and female deer, and the increase of head size in older males are possibly responsible for this. There were low densities of C. auribarbis while P. picta was the species most frequently observed, although both oestrids were located in the same host cavities. The earlier larviposition by C. auribarbis, and its faster larval development may reflect asynchronous life-cycles of both oestrids; this may decrease inter-specific competition between these sympatric species.