We investigate changes in small-mammal richness and diversity in southwestern Europe (Iberian Peninsula) during the late Pleistocene–Holocene transition in order to evaluate whether they follow a climatic pattern or are predominantly determined by human impact, especially after the emergence of agriculture in the Neolithic period. We selected 6 late Pleistocene and Holocene sites that correspond to 18 different layers dated to between ca. 22 and 3 kyr B.P. Using indices of species richness and evenness diversity, we show that climate played an important role at some sites during the late Pleistocene and at the beginning of the Holocene, in that the richness and diversity of small mammals were closely related to the mean annual temperatures and landscape changes, and varied according to the different climatic fluctuations detected (Heinrich Event 1, Bølling-Allerød, and Preboreal-Boreal). However, at the beginning of the mid-Holocene, the small-mammal richness and diversity no longer seem to follow any kind of climatic pattern, and the observed changes in some studied sites are more closely related to human activities. By contrast with similar studies carried out in other parts of the world, the changes in diversity in the Iberian Peninsula do not seem to follow a constant pattern during the late Pleistocene and beginning of the Holocene. Some of the changes detected appear to be related to climate (late Pleistocene), and others appear to be related to human influence (Holocene) on the landscape.