Tapeworms (Cestoda) of the Proteocephalus-species aggregate from cyprinoids, pike, eel, smelt and cavefish in the Nearctic region (North America) are reviewed, based on a critical examination of newly collected and museum specimens. For some species neither new nor museum specimens were available and only literature data were used for these taxa. Two species occur in North American cyprinoids: (i) Nearctic Proteocephalus buplanensis Mayes, 1976 in Semotilus atromaculatus (Mitchill) in the upper Mississippi River and Hudson Bay drainage basins, and (ii) Holarctic P. torulosus (Batsch, 1786) (syns. P. ptychocheilus Faust, 1919; P. cobraeformis Haderlie, 1953; and Ophiotaenia critica Mpoame & Landers, 1981, new synonym), which occurs in Ptychocheilus spp. and other leuciscids in the western part of North America. Proteocephalus pinguis La Rue, 1911 is a specific parasite of pike (Esox spp.), which is briefly redescribed here to establish its diagnostic morphological characteristics because the original description was based on a mixture of at least two species. In addition to P. pinguis, pike serve as postyclic hosts of several species of the Proteocephalus-aggregate typical of other fish, such as bass, perch and whitefish, namely P. fluviatilis Bangham, 1925, P. pearsei La Rue, 1919 and P. longicollis (Zeder, 1800). Cavefish (Amblyopsidae) in North America harbour two endemic species, P. chologasteri Whittaker & Hill, 1968 from Chologaster agassizii Putman and P. poulsoni Whittaker & Zober, 1978 from Amblyopsis spelaea DeKay, which have never been found since their original description and their validity should be confirmed based on new collections and molecular data. Two other species of the Proteocephalus-aggregate, P. macrocephalus (Creplin, 1825), a parasite of eels (Anguilla spp.), and P. tetrastomus (Rudolphi, 1810) from smelt (Osmeridae), have circumboreal (Holarctic) distribution. Molecular data are available only for three of the seven species treated herein, but they do not form a monophyletic group.