Spatial genetic structure in white-tailed deer (Odocoileus virginianus) has been examined at regional scales, but genetic markers with the resolution to detect fine-scale patterns have appeared only recently. We used a panel of microsatellite DNA markers, radiotelemetry data, and visual observations of marked deer to study fine-scale social and genetic structure in a high-density population of white-tailed deer (12–20 deer/km²). We collected genetic data on 229 adult females, 102 of which were assigned to 28 social groups. Our results were consistent with the conceptual model of white-tailed deer social structure, where philopatric females form social groups composed of related individuals. Within-group relatedness values approached the expected value for 1st cousins (R  =  0.103, SE  =  0.033), but individuals among groups (R  =  −0.014, SE  =  0.003) and overall (R  =  −0.009, SE  =  0.003) were unrelated. Fixation indices revealed a significant departure from equilibrium values among social groups (F_ST  =  0.076, SE  =  0.007) and an excess of heterozygotes within groups (F_IS  =  −0.050, SE  =  0.018), consistent with theoretical expectations for mammal populations characterized by female philopatry and a polygynous mating system. Analyses of spatial autocorrelation indicated genetic structuring occurred at a very fine spatial scale, where pairs of adult females within 1 km were genetically nonindependent. The occurrence of fine-scale genetic and social structure has implications for the ecology and management of white-tailed deer, including habitat use and resource competition, offspring sex allocation theories, disease transmission, and the consideration of social behaviors in management.