During 1982, 3,095 social groups of white-tailed deer (Odocoileus virginianus) were observed in Shenandoah National Park, Virginia. Both time of day (dawn, day, dusk, and night) and season of the year (spring, fawning, summer, breeding, and winter) had a significant effect on total deer/ group and numbers of adults, adult females, and adult males. Group size was largest at dusk (mean 2.7, range of 1 to 28), and slightly smaller at night (2.4, 1 to 21), at dawn (2.3, 1 to 10), and during the day (2.3, 1 to 13). Seasonally, group size was largest in winter (mean 3.4, range of 1 to 28). noticeably smaller during breeding (2.5, 1 to 13) and spring (2.4, 1 to 9), and smaller still during late summer (2.0, 1 to 10) and fawning (1.7, 1 to 9). Time of day did not significantly affect occurrence of doe, buck, and mixed groups, but season did, with doe groups occurring most frequently (90% of all observations) and buck groups least frequently (4%) in winter than during any other season. Single adult females were most common (27% of all observations), followed by 1 adult female with 1 fawn (13% ), a single adult male (7%),2 adult does (6%), and 2 does with 1 fawn (6%). At least 1 adult was present in 93% of all social groups. Adult does exhibited a moderately high degree of mutual tolerance at all times of year except the fawning season.