The Manx shearwater flea Ceratophyllus (Emmareus) fionnus Usher, 1968 is a host-specific parasitic insect apparently restricted to the Isle of Rùm, off the west coast of Scotland. Although C. (E.) fionnus is one of only a small number of insect species endemic to the British Isles, its conservation status has never been evaluated. To enable effective management, the conservation status of the species was assessed.The conservation status of C. (E.) fionnus was evaluated using host and distribution records in conjunction with two assessment rubrics; the IUCN Red List Categories and Criteria: Version 3.1, and a flea-specific assessment rubric developed previously.Ceratophyllus (Emmareus) fionnus was found to be threatened with extinction due to its hyperendemicity on the Isle of Rùm and was classified as vulnerable.Based on the findings of the assessment, immediate conservation action to protect C. (E.) fionnus is encouraged and a recovery plan is outlined. This includes surveys and studies of the bionomics of the species in conjunction with in-situ management of the known population. The creation of insurance populations through conservation translocations is also encouraged.