Late Cretaceous to Early Paleocene ostracode assemblages in the SE Netherlands and contiguous areas of Belgium underwent several event-induced changes in their qualitative and quantitative composition. The first change took place between the Early and Late Campanian and is marked by the appearance of several new taxa, many of which belong to Cytherelloidea and Bythoceratinae . The event causing this obvious diversification may have been either a deepening of the sea or a warm-up of the marine environment. The second important change during the mid-Late Maastrichtian seems related to the relaxation of regional inversion tectonics and a concomitant massive invasion of Tethyan elements. Finally, the third event at the Maastrichtian-Danian (Cretaceous-Tertiary) boundary is distinguished by a practically complete species turnover and the disappearance of eighty percent of the Late Maastrichtian ostracode genera from the area. However, at least some fifty percent of these genera survived elsewhere in the northern Tethys. This illustrates that the drastic change in the ostracode faunas of the SE Netherlands was caused by changes in the regional environment of NW Europe and not by a massive, global extinction event.