European chestnut (Castanea sativa Mill.) is one of the most known trees occurring in Europe. Therefore history of spread of the species on this continent is a subject of interest of many authors. At present this species is naturalized in southern and middle Europe. In Poland it is often cultivated in parks, gardens but it has not been treated as a permanent element of the Polish flora so far. The closest localities, where it is naturalized, are in Czech and middle Germany. In the years 2000-2005 spontaneous spread of the species on the Baltic coast in urban sites (town of Łeba, 54 [deegres] 4.N, 17 [deegres] 33.E) was observed, where its population amounts to one hundred of individuals dispersed up to 600 m. This is the first locality of Castanea sativa in Poland, where it occurs spontaneously. This finding would probably enable to move the border of European chestnut range in Europe towards northern-eastern direction by several hundreds kilometers.