Wolves (Canis lupus) belong to 3 genetically distinct subpopulations despite the absence of topographic barriers limiting dispersal. Based on data on wolf diets from 13 localities and wolf kill remains from a national-scale census, we investigated regional variation in wolf diet in relation to species structure of ungulate communities and spatial genetic differentiation of wolf populations. We also tested if various sources of data on wolf prey (scats and kills) and availability of ungulates (game inventory and harvest) yielded comparable results on prey selection. The main prey of wolves was red deer (Cervus elaphus), roe deer (Capreolus capreolus), and wild boar (Sus scrofa). The proportion of main prey in wolf diets increased with prey availability in the community, yet wolves selected red deer, preyed on roe deer proportionally to their relative abundance, and avoided wild boar. Large prey was recorded among kills more often than small prey. Despite similar species structure of ungulate communities throughout Poland, there were significant regional differences in wolf diet, which corresponded to the genetic structure of populations. In northeastern Poland, wolves frequently hunted red deer, roe deer, wild boar, beavers (Castor fiber), and moose (Alces alces). In eastern Poland, roe deer dominated kills. In southeastern Poland, wolves were strongly specialized on red deer. We propose that prey and habitat specialization of wolves, rather than geographic distance or topographic barriers to dispersal, are responsible for the observed ecological divergence of wolf populations, as reflected in their diet composition.