Silene borysthenica is a species typical for psammophytic grassland. In Poland it is very rare and endangered, due to the abandonment of traditional grazing and to direct destruction of its habitat (afforestation, urbanization). Only a few of its localities known in the 20th century have been confirmed recently. In 2015 a new locality of S. borysthenica near Wyszków in the Bug River valley was found, and in 2016 a locality probably known previously, near Wieliszew close to Zegrzyńskie Lake, was confirmed (Fig. 1, Tabs 1, 2). The species may vanish from both localities in the coming years as a result of many potential threats, including succession toward forest vegetation (both localities), uncontrolled use of motorbikes and quads in the area (Wyszków), and reconstruction of a railway track which is planned for the near future (Wieliszew). Collection of seeds from both populations is highly recommended, to ensure at least ex situ protection of the Polish S. borysthenica populations.