Marine reptile remains occur in the Upper Cretaceous (lower Campanian to lower Maastrichtian) Adaffa Formation of NW Saudi Arabia. This is the first detailed report of late Mesozoic marine reptiles from the Arabian Peninsula. The fossils include bothremydid (cf. Taphrosphyini) turtles, dyrosaurid crocodyliforms, elasmosaurid plesiosaurs, mosasaurs (Prognathodon, plioplatecarpines) and an indeterminate small varanoid. The assemblage is compositionally similar to contemporary faunas from elsewhere in the Middle East/North Africa, and comprises taxa that are typical of the southern margin of the Mediterranean Tethys.