The Acanthocephala constitute a group of helminth parasites that, as adults, infect all classes of vertebrates. Adults of Neoechinorhynchus brentnickoli are parasites of Dormitator latifrons, a commercially important fish species in Tres Palos Lagoon, Guerrero, Mexico. The aim of this study was to describe features of the reproductive biology of this acanthocephalan. Fish were collected from Laguna de Tres Palos during February 2012 to February 2013. The number of fish that were examined (n = 688) ranged from 35 (June) to 70 (August) in each collection. The prevalence of infection was more than 90% during this period and mean abundance varied significantly from 32.3 worms per fish (July 2012) to 89.3 worms per fish (March 2012). Acanthocephalans were reproductively active during the whole year. The stomach was the region of the digestive tract with the smallest percentage of helminths, and females were more abundant than males in all sections of the intestine. Larger male and female worms were always located in the more posterior sections of the digestive tract. The mean length at which 50% of individuals reached sexual maturity was 2.9 mm for females and 2.3 mm for males. Relative fecundity increased with length in females.