Field studies conducted in 2005–2018 yielded information about the distribution and condition of Arenaria graminifolia (Caryophyllaceae) in Kampinos National Park (central Poland). Arenaria graminifolia was found at four new sites located in Łuże, Biała Góra, Krukowa Góra and Czerwińskie Góry. Historical stations from Krzywa Góra and Łużowa Góra were not reconfirmed. Arenaria graminifolia was found in squares ED1536, ED1378 and ED1205 of the ATPOL cartogram of 1 × 1 km grid squares. The sites in the study area are shown in Figure 1. The paper gives information on the locations of the recorded species, its characteristics, habitat conditions, plant communities and numbers found, and threats and protection issues are discussed. Arenaria graminifolia is found in forest areas, in open pine forests, on dry ground, usually on the southern slopes of dunes with a slight slope. The plant communities belong to pine forest of the Dicrano-Pinion alliance (fresh Peucedano-Pinetum forest) or mixed fresh Querco roboris-Pinetum association. In addition to a significant share of species from the class Vaccinio-Picetea, shares of species from the classes Koelerio- Corynephoretea and Nardo-Callunetea are also marked (Tab. 1). The Arenaria graminifolia populations vary greatly in abundance, from several hundred (Biała Góra) to over three thousand vegetative shoots in the Łuże region. Generative individuals form up to 5% of the population. The entire population of A. graminifolia in Kampinos National Park numbers 5310 shoots. Arenaria graminifolia in Poland has been known from only 29 stations. Many of the stations recorded in the 19th and 20th centuries are historical, so it has been considered a critically endangered (CR) species (Jakubowska-Gabara 2014; Kaźmierczakowa et al. 2016).