This article presents new evidence on the evolution of regional inequality in Iberia from 1900 to 2000 from a geographical perspective. To do so we introduce a new historical dataset of regional gross domestic products (GDPs) for Spanish NUTS III and Portuguese Historical Districts, synthetic indices of regional inequality, and different measures of spatial correlation across regional per capita GDPs. The results show that the Portuguese and Spanish national economic integration processes initially led to the economic specialization across Iberian regions promoting the divergence in terms of their regional per capita GDPs. Notwithstanding, ulterior advances in the integration of national markets and the subsequent first stages in the process of adhesion of these two national economies into the UE coexisted with a progressive reduction in Iberian regional inequality.