Bottom sediments of Lake Łańskie in NE Poland (Olsztyn Lake District) were studied by pollen analysis, and vegetation changes from ca 4800 BC to modern times were reconstructed based on the results. Due to rapid sedimentation the changes in plant cover are recorded with high resolution. The variation of pollen spectra composition reflects changing shares of deciduous trees and the continuous dominance of pine forest. Nowadays the surroundings of Lake Łańskie are also heavily forested but as early as 1100 AD the deciduous trees began to be eliminated. On the basis of pollen data, five phases of increased human activity were distinguished. Based on the available archaeological chronology of local settlements, the first stage is connected with para-Neolithic groups of Ząbie-Szestno type and the Lusatian culture. They are followed by the West Baltic Barrow culture, Wielbark culture and Early Medieval Prussian tribes. The pollen record shows low intensity of exploitation of the terrain around Lake Łańskie, probably attributable to the brevity of episodes of human occupation in the near vicinity of the lake. The last phase, covering part of the Middle Ages (since ca 1000 AD) and modern times, is reflected in the most distinct vegetation changes on the pollen diagram, caused by increased intensity of settlement. In spite of the distinct diminution of forest cover around the lake the scale of deforestation was much lower than at other sites in NE Poland. The main aims of this paper were to describe the changes in the palaeoenvironment which took place around Lake Łańskie (Olsztyn Lake District) and to find those changes in the plant cover which were the effect of human activity, and to confirm whether the changes of palaeoenvironment around Lake Łańskie were noted at the same time in adjacent areas.