We studied daily activity patterns of 19 (7 males and 12 females) adult red deer (Cervus elaphus) by using continuous tracking sessions in Białowieża National Park (BNP), Poland, from 2001 to 2004. Male and female red deer were active throughout the day and night during all seasons, with several peaks in activity during the 24-h period, although both sexes tended to be more active during the day in winter. There were no significant differences between males and females in mean time active (8 h/day for both sexes), mean length of activity bouts (42 min), and mean number of activity bouts (12 bouts/day). Additionally, neither sex showed seasonal differences in hours active, bout length, or number of bouts per day. However, rainfall affected activity of males, whereas ambient temperature and snowfall affected activity of females. Although red deer are sexually dimorphic, which often leads to differences in movements and social groupings, our results suggest that their general activity patterns are influenced less by these sexual differences and more by the constraints of feeding and rumination, daily abiotic factors, and possibly predation risk from wolves (Canis lupus). Red deer in BNP did not exhibit strong bimodal peaks in activity at dawn and dusk as shown in previous studies, likely because strict limits on human activities in BNP allowed red deer to base their activity more on natural factors than on human-related factors.