Probothriocephalus alaini n. sp. is described from the intestine of the deep-sea fish Xenodermichthys copei (Gill) (Osmeriformes: Alepocephalidae) from the North Atlantic. It resembles most closely the type-species of Probothriocephalus, P. muelleri Campbell, 1977 described from Alepocephalus agassizi Goode & Bean (Alepocephalidae), but it differs in the distribution of the vitelline follicles that form two medially well-separated bands (versus almost circum-cortical in P. muelleri), in the shape of gravid proglottids that are elongate, much longer than wide (always wider than long in P. muelleri), in the size of the body (much larger in the latter species) and a somewhat different shape of the scolex (widely lanceolate versus elongate and tapering anteriorly in P. muelleri). Other congeneric species, described from deep-sea fish of different orders (Myctophiformes and Beryciformes), lack a distinct neck region, their eggs were reported to be non-operculate and they have much more pronounced external segmentation.