Human activities can affect the behavior and well-being of wildlife, and there is high potential for wildlife disturbance due to human outdoor recreation. Hiking is a popular form of outdoor recreation in many countries, including Germany. In this study, we investigate the effects of hiking and hiking trails on space-use dynamics in GPS-collared red deer Cervus elaphus inhabiting the Kellerwald-Edersee National Park, Germany. Specifically, we 1) experimentally assess the reactions of red deer to hiker on- and off-trail and 2) quantify the effects of hiking trails on daily space-use patterns of the deer. We found that red deer in the Kellerwald-Edersee National Park did not show a spatiotemporal reaction to recreational on-trail hiking, but were sensitive to off-trail hiking that always induced flight of the animals. With increasing trail densities, the flight initiation distance decreased, while the distance moved during a flight was similar across trail densities. Together, these results suggest that the sensitivity to off-trail hiking increases in areas with low trail density, but that the flight reaction, once induced, is uniform. We further demonstrate that red deer avoid hiking trails during the day, but not during nighttime, and that a negative relationship exists between the distance the animals keep to trails and the trail density in an individual home range. Our results indicate that off-trail hiking has the potential to disturb red deer in the Kellerwald- Edersee National Park, but that red deer are able to cope with recreational activity on trails as well as with the presence of trails in general. Our findings underline the importance of hiking rules, such as staying on trails, and visitor management focusing on minimizing conflicts between wildlife and human recreation.