The extant wild boar Sus scrofa has one of the largest geographical range of all mammals, and from its appearance in the late Early Pleistocene (Epivillafranchian) it is also widely represented in the European fossil record. Early forms of the species were larger than Late Pleistocene ones, but neither the chronology nor the causes of the size reduction have been thoroughly investigated. Here, we considered for the first time a large number of fossils from several late Middle Pleistocene to Early Holocene sites of the Apulian region (Italian Peninsula). In contrast to the supposed existence of a progressive trend towards small dimensions, morphometric comparisons and body mass estimates allow us to recognize several size oscillations during the late Middle Pleistocene-Early Holocene, with large forms occurring during interglacial stages and smaller ones during glacial stages. This suggests that fossil Apulian wild boar did not conform to Bergmann’s rule, that predicts larger size in colder climates due to the selective pressure towards lower surface area to volume ratio. Climate recrudescence may have played an indirect role in reducing the availability of trophic resources and hence promoting the observed pattern.