Neoechinorhynchus brentnickoli n. sp. is described from specimens of Dormitator latifrons (Pacific fat sleeper) collected from 3 localities along the Pacific Coast of México: Tres Palos Lagoon (Guerrero State), Bahía de Chamela (Jalisco State), and Mazatlán (Sinaloa State), México. Of the 3 members of the genus known from Mexican fish, the new species is more similar to Neoechinorhynchus golvani Salgado-Maldonado, 1978, than to Neoechinorhynchus roseus Salgado-Maldonado, 1978, or Neoechinorhynchus chimalapasensis Salgado-Maldonado, Caspeta-Mandujano, and Martínez-Ramírez, 2010. Neoechinorhynchus brentnickoli n. sp. can be distinguished from N. golvani in being longer and having more dimorphism between trunk length of males and females, a different number of ventral giant nuclei (2 vs. 1), smaller proboscis, shorter hooks in all 3 circles, a longer receptacle, and larger testes and cement gland. The anterior portion of the trunk wall of the new species is more delicate than that of the rest of the trunk, and it can be inverted into the body cavity in a manner similar to the way in which the proboscis is inverted into the receptacle. Previous studies that attributed specimens of this species to N. golvani are discussed.