Cryptobranchus guildayi has been described as an extinct species of large salamander that is related closely to the modern Hellbender, Cryptobranchus alleganiensis. The validity of this extinct taxon has been questioned; thus, an expanded osteological sample of modern Hellbenders was compared to the C. guildayi fossil material. Based on our analysis of the fossil material, all morphological characters used to define C. guildayi can be observed in specimens of C. alleganiensis, or are based on misidentifications. Therefore, C. guildayi is considered to be conspecific with C. alleganiensis and taxonomically should be considered a junior synonym of the latter. The reassignment of the C. guildayi specimens to C. alleganiensis expands the prehistoric geographical range of the modern species to the Potomac River and its tributaries and also extends the age of the species into the Irvingtonian North American land mammal age.