Sediments of the Méndez Formation near Cerralvo, Nuevo León, northeastern Mexico, yield an abundant and diverse Maastrichtian ammonite assemblage. A total of 24 species referred to 18 genera are present, in addition to the possible coleoid Naefia neogaeia Wetzel. The assemblage is considered to be of late early Maastrichtian age on the basis of ammonite occurrences and has been dated to the Gansserina gansseri Zone (Zone CF 7 of Li and Keller 1998a, 1998b) by planktic foraminifera. None of the ammonite species has been reported previously from the Méndez Formation and most species are here recorded for Mexico for the first time. In addition to faunal elements known from other Gulf of Mexico localities (e.g., N. (Nostoceras) colubriformis, N. (N.) alternum, N. (N.) rugosum, Baculites ovatus, Solenoceras reesidei) the assemblage is characterised by cosmopolitan (e.g., Phyllopachyceras forbesianum, Pseudophyllites indra and Diplomoceras cylindraceum) and Tethyan elements (e.g., Baculites vertebralis, Fresvillia constricta, Anagaudryceras politissimum, Gaudryceras kayei, Hauericeras rembda, Anabrahmaites vishnu, Menuites fresvillensis). In addition, ammonite species are present hitherto known from the Indopacific region and southern high latitudes (e.g., Neophylloceras (Hypophylloceras) hetonaiense, Gaudryceras kayei, Anagaudryceras politissimum, Zelandites varuna, Fresvillia teres).