The association between genetic structure and social structure was investigated in a free-ranging population of white-tailed deer (Odocoileus virginianus) in northern New York. Social groups were differentiated based on spatial aggregations and allozymic characteristics (P < 0.05). Genetic structure was evident despite the high probability that males interbreed among adjacent and overlapping social groups on summer range. An excess of heterozygosity occurred within groups (FIS = −0.25) relative to that expected from Hardy-Weinberg proportions. We suggest that the excess may be accounted for by a high turn-over rate among breeding males who lose their dominance between years. Genetic distances among groups were associated with the location of the social group on winter range. Groups that used the same winter range were more genetically similar even though in the central Adirondacks deer primarily breed on their summer range. We suggest that this association with winter range is due to the traditional use of winter yards by matrilineal groups and is maintained by female philopatry.