Studies on diurnal activity and factors affecting the questing behavior in Dermacentor reticulatus (F.) adults were conducted in an open-type habitat in eastern Poland (51° 15′ N, 22° 36′ E). Observations, for 25 min each, were made at 2-h intervals between 1000 and 1800 hours, during the autumn (from late September to mid-October 2000) and spring (from late April to mid-May 2001) activity peaks. The questing behavior of adult D. reticulatus ticks depended on the time of the day and season. The autumn activity was higher than that in spring, yet both these periods were characterized by a rising trend from the morning to early afternoon with a peak at ≈1400 hours (on average 40 and 30 specimens per one collection, respectively). In spring, the high activity (on average 31.8 specimens/ collection) persisted until late afternoon (1800 hours), while in the autumn period it declined before nightfall (on average 21.4 specimens/collection at 1800 hours). Females predominated over males in both seasonal periods of activity and greater differences in the sex ratio were recorded in the spring. We found a negative correlation between the diurnal activity of the adult ticks and temperature and between the number of active ticks and the length of day both in the autumn and spring. However, no statistically significant correlation was demonstrated between the diurnal activity of adult ticks and humidity. The investigations show that, in addition to environmental factors, tick host-seeking behavior is dependent on the activity of their hosts and biological traits of this species.