The aim of this work is to study the characteristics of the traditional fiscal systems (forales), the possible gains they generate in capacity and the viability of extending them to other autonomous regions. The traditional system in force in the autonomous region of the Basque Country and the results of the five-year period 1987-1991 constitute the basic scope of reference. The study analyzes the financial flows between central government and the territories with the special system and lays particular emphasis on the cupo (own tax collection regime). In addition, the research highlights that the traditional fiscal systems produce a financial capacity that is much higher than that achieved with the normal system. Finally, it nevertheless establishes that generalizing a foral system such as in the Basque Country is not viable from a financial point of view because it would substantially reduce the funds available to central government.