We compiled information on freshwater Nematomorpha (horsehair worms) from North America including new records of more than 100 specimens from 66 new locations and the description of two new species. From the 30 species names that have been used for Nearctic nematomorphs, 15 are regarded as valid species. The descriptions of most of these species were supplemented with new material and documented by light and scanning electron microscopy. Three species, Gordius agassizi, Gordius fasciatus and Gordius hawaiiensis are synonymized with Gordius robustus. Gordius leidyi is not a valid species, but its assignment is uncertain. Gordius tenuis is not a nematomorph, but a mermithid nematode. Parachordodes densareolatus is a questionable species and might belong to Gordionus. New combinations are given for three species. The two new species described here raise the number of gordiids known from the Nearctic region to 17. A taxonomic key and a geographic list of species distributions are given in appendices.

Species novae: Gordionus sinepilosus (British Columbia, Canada), Pseudochordodes texanus (Texas, U.S.A.).