A total of 48 adults Pacific fat sleepers Dormitator latifrons was collected from Tres Palos Lagoon, Guerrero, Mexico, between May and August 1999. Seven helminth taxa were recovered: Clinostomum complanatum, Pseudoacanthostomum panamense, Saccocoelioides sp., Neoechinorhynchus golvani, Contracaecum sp., Cosmocerca podicipinus and Gnathostoma sp. All of the Pacific fat sleepers were infected. Mean species richness and mean helminth abundance were 2.4 and 143.6, respectively. Helminth infracommunity diversity was low (with a Brillouin's value of 0.6), reflecting the high proportion of the sample dominated by N. golvani (48%) as well as the larger number of metacercariae of P. panamense. These characteristics were similar to those previously observed in other brackish water fishes. Three essential factors determine the helminth infracommunity of D. latifrons: diet, feeding behavior and vagility of the host. Additionally, the composition of helminth fauna is also influenced by the oligohaline condition of the lagoon (4 of 7 species have freshwater origin).