Oochoristica whitfieldi n. sp., parasitizing the intestine of the Oaxacan black iguana Ctenosaura oaxacana (Kohler and Hasbun, 2001), in Ruinas de Guiengola, Oaxaca state, Mexico, is described. The new species can be distinguished from all 4 congenera infecting Iguanidae in the neotropical realm in possessing a lower mean number of testes (122 in O. acapulcoensis Brooks, Pérez-Ponce de León, and García-Prieto, 1999; 62 in O. guanacastensis Brooks, Pérez-Ponce de León, and García-Prieto, 1999, and 95 in O. leonregagnonae Arizmendi-Espinosa, García-Prieto, and Guillén-Hernández, 2005, vs. 35 in O. whitfieldi), and a wider scolex (0.450–0.600, 0.475–0.537, 0.5–0.8, vs. 0.25–0.26, respectively). Oochoristica iguanae Bursey and Goldberg, 1996 differs from the new Mexican species in having a longer strobila (60–110 mm vs. 14.4–33.7 mm, respectively), fewer ovarian sublobes (6 vs. 11–17), and a cirrus pouch that hardly reaches excretory canals (whereas in O. whitfieldi the cirrus pouch widely overpasses these canals).