In the last two years, as part of the ’ANM-project’ (Atlasproject Nederlandse Mollusken), the occurrence of Vertigo moulinsiana (Dupuy, 1849) in the Netherlands is under investigation. This highly specialised and threatened landsnail, once thought to have completely dissapeared from the Netherlands, now only occurs in a few very small marshes in the south of the province of Zuid Limburg. Data are given on recent, earlier and fossil occurrences. Also the habitat, vegetation and several other essential parameters are discussed. In a follow-up article (page 19) measures for protection and maintenance of habitat are discussed.