Fossil teeth of the genus Megachasma Taylor, Compagno & Struhsaker, 1983 are recorded for the first time in Europe. Isolated teeth have been recovered from the transgressive layer at the base of the Belgian Pliocene, extending the known paleogeographic range of this genus. These teeth are compared with fossil specimens from Greece, Chile, USA and extant specimens. The Belgian teeth seem to fit well in the gap between the early Miocene teeth from California and those of the extant taxon Megachasma pelagios Taylor, Compagno & Struhsaker, 1983; while the megamouth teeth found in Late Miocene to Early Pliocene sediments worldwide (Chile, North Carolina, Florida, and Greece) appear to be giant versions of modern teeth. Juvenile teeth of modern Megachasma pelagios are illustrated for the first time, showing a distinct ontogenetic variation in the roots and crown surface.