Diet, carcass weight (dressed weight) and kidney fat index (KFI) in wild boar populations were compared between two different lowland environments in south-western Poland. In the forest-farmland environment of the Lasy Śląskie forest (LS), fodder root crops and cereals made up 67.6 % of the dry weight (d.w.) of stomach content (n = 40). In the large compact forest of the Bory Dolnośląskie forest (BD), 69.6 % of the stomach content (n = 43) was made up of roots and browse. Piglets and older animals harvested in BD were significantly lighter than those harvested in LS (13.6 kg vs. 25.6 kg and 47.3 kg vs. 55.9 kg respectively). The KFI of piglets and older animals harvested in LS were significantly higher than those in corresponding age classes of wild boars from BD. The metabolized energy of stomach content amounted to 13.2 MJ/kg d.w. in LS and 8.9 MJ/kg d.w. in BD. This is probably the chief cause of the differences in carcass weight and KFI between the wild boars living in the compared study areas.