The Christmas Island shrew (Crocidura trichura), endemic to Christmas Island in the Indian Ocean, was abundant at the time of the island's settlement in the 1890s. However, since 1900, it has been reported only four times (twice in 1958, 1984 and 1985). It is currently considered Critically Endangered under Australian law. Using a recently developed IUCN protocol (the 'Records and Surveys Model'), based on compilation and assessments of targeted and general sampling effort and detectability, we estimated that there is a 96.3% likelihood that the species is now extinct. However, although many general survey methods (including inspection of cat gut samples, ink cards, audio-recording, pitfall traps, spotlighting and camera traps) have been employed on Christmas Island, most recent sampling has not been targeted specifically to detect this species. Furthermore, there is considerable uncertainty about its likely detectability with different sampling techniques and hence much uncertainty about the estimate of likelihood of extinction. e-DNA sampling, use of detector dogs and refinements in audio-recording may help increase the likelihood of detection, if present. Most current conservation management actions, undertaken for other threatened species on Christmas Island, would provide benefit to the Christmas Island shrew, if it is extant.