Northwestern Deermouse (Peromyscus keeni) is distributed on several islands of Haida Gwaii, British Columbia, but its absence from Langara Island has puzzled biologists who wondered whether the introduction of rats (Rattus spp.) contributed to its extirpation. An often-cited reference to naturalists' visits to Langara Island in the 1930s, before the introduction of rats, noted that deermice were common, but details of observations were lacking and specimens were not mentioned. Scrutiny of the literature and archived field notes, and inquiries with museum curators, yielded no evidence for the historic presence of deermice on Langara Island. Details pertaining to 1 specimen taken on Langara Island during rat-eradication activities, in 1994, plus 1 encounter with a live deermouse in a seabird burrow in 1966 provide the only records of the occurrence of Northwestern Deermouse on Langara Island.