A redescription of the male and the first description of the female of the intestinal nematode Capillaria carioca Freitas et Lent, 1935 are presented on the basis of specimens collected from the type host, the marine fish Sphoeroides testudineus (Linnaeus) (Teleostei, Tetraodontoidei), from the Lagoon of Yucalpetén in the northern coast of Yucatan (Gulf of Mexico), Mexico. This species is characterized by a well-sclerotized spicule and by the presence of two large ventrolateral lobe-like papillae on the male caudal end and, therefore, is assigned to the subgenus Neocapillaria Moravec, 1987. C. carioca is reported from Mexico for the first time.