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Earlier reports suggest a distinct pattern of genetic variation linked to both language and geographic distance in Island Melanesia. Inland Papuan-speaking populations from different islands tend to share one allelic profile, while shore-based or more cosmopolitan populations share another, related to Southeast Asian influence over the past 3000 years. In the present paper, we report the genotypes and allele frequencies of an informative 9.1- thousand-base-pairs (kb) insertion/deletion polymorphism in 19 populations living in Island Melanesia. The populations studied inhabit the islands of New Britain, New Ireland, New Hanover, and Mussau in the Bismarck Arch- ipelago, and speak either Austronesian or Papuan languages. We also include for reference a collection from New Guinea and Bougainville. The data show a marked fluctuation in the allele frequency among the different isolates, with the 9.1-kb(–) allele frequency ranging from 0.67 to 0.98. The deletion allele reaches fixation in some Papuan-speaking interior populations of New Britain, as well as in the interiors of New Guinea and Bougainville. However, certain inland Austronesian-speaking populations also share a similar high frequency of the deletion. Our data suggest that language distinctions are generally, but not invariably, indicative of diverse allelic patterns in this com- plex region, where inland groups on large islands tend to be often distinctive from shore-based populations.