We present the first thorough revision of the continental mollusc fauna from the early Middle Miocene wetlands of the Rein Basin (Styria, Austria). Lake Rein was a shallow ephemeral lake with carbonate sedimentation. Its mollusc assemblage comprises 13 species and is dominated by planorbid gastropods in species and individual numbers, accompanied by lymnaeids and rare hydrobiids. The terrestrial assemblage consists of 35 species with Discidae, Elonidae and Helicidae as most abundant taxa along with carychiids. The terrestrial gastropods suggest moist woodland and only limited areas of open habitats; the freshwater species point to stagnant and shallow water bodies with dense vegetation and only very limited fluvial input. Many taxa are illustrated for the first time and historical mis-identifications are corrected. About one third of the species is known so far from the Rein Basin only, but the majority of the species is also known from other Middle Miocene lakes and wetlands of Central Europe. The strongest faunistic relations are indicated with the Badenian wetlands of the Paratethys Sea and the so-called Silvana-beds of Southern Germany.