In the course of a parasitological survey carried out on Greenland halibut, Reinhardtius hippoglossoides (Pleuronectiformes) from the eastern part of the Bering Sea (North Pacific) a single specimen of a monogenean fluke was found. The parasite, later identified as Pseudacanthocotyla williamsi (Price, 1938) Yamaguti, 1963 has never been found on a Greenland halibut. This fish species has been considered an atypical host for all monogeneans of the family Acanthocotylidae. The present work contains a detailed redescription of the parasite found.