Seasonal vanatlOns in sex ratio and group compositIOn of white-tailed deer (Odocoileus virginianus) were studied on the Welder Refuge, Texas. Group size varied from 3.2 to 7.3 with a mean of 4.9. Sex ratio (0 to <;> ) varied from 27:100 to 42:100 with a mean of 35:100. Group composition also varied throughout the year, due to variations in reproductive behavior. Data indicate that total counts are best conducted in April but sex ratios are best determined in August. The purpose of this paper is to describe the seasonal associations of whitetailed deer with emphasis on evening feeding groups. Several authors (Davis 1963, Hanson 1963, Wight et al. 1965, Rupp 1966) have pointed out that a knowledge of both real and apparent fluctuations is essential when changes in sex and age ratios are used to improve our understanding of population dynamics and management. Factors affecting seasonal variations in group size and composition are especially important in interpreting these fluctuations. Biases which occur due to contrasting behavior of sex and age classes are recognized but there is a paucity of data showing specific differences. Hawkins and Klimstra (1970), in one of the most detailed studies on social organization of white-tailed deer, showed that seasonal variations in associations, group size and composition, movements, and spatial relationships were deeply established. Jahn (1959) suggested that differences in behavior led to seasonal variations of road-killed deer in Wisconsin; Dasmann and Taber (1956) discussed the seasonal variation in family groups of mule deer (0. hemionus) in California; and Martinka (1969) presented a description of seasonal variation' in composition of elk (Cervus canadensis) in Wyoming.