Large mammals are often a source of conflict, and consequently there has been increasing interest in close encounters with them. Knowledge of wildlife responses to human disturbance is crucial for the management of increasing and expanding populations of large animals. We investigated flight initiation distance (FID) and aggressive responses of the European bison-the largest terrestrial mammal of Europe-to human disturbance in the Białowieża Forest (NE Poland). When encountered by humans, bison usually flee. Aggression was observed in only 0.4% of approach attempts. Mean FID was 77±46 m and was influenced by habitat, sex, and supplementary feeding intensity. Females showed greater timidity than males, FID was lower in forest than in open habitats, and supplementary feeding caused a drop in FID. In 84.5% of all documented aggression cases, bison attacks were provoked by humans approaching too close to the bison or by deliberate scaring them. Males were more aggressive than females, and attacked mainly during the rut, while females attacked during the winter and calving. Bison attacked in built-up areas significantly more often than expected. The mean critical distance of attacks was 21±2 m. Most attacks took the form of a short chase preceded by warning signs. Goring was observed in 22.7% of all aggression cases and no fatalities were recorded. Our study shows that bison are not dangerous animals and only manifest aggression in response to prolonged disturbance at close ranges. The education of people and recommendations for minimum approach distances should ensure a low rate of disturbance and safety when encountering large mammals.