This paper is concerned with the existence and the salient characteristics of an extensional shear zone (the Puente Génave-Castelo de Vide shear zone) along 400 km in the southern Central Iberian Zone. This shear zone is almost parallel to the previous Variscan structures, but it is slightly cross-cut by the discontinuous late Carboniferous Alburquerque-Pedroches batholithic alignment (which has been considered by some authors to be a fundamental feature for the sub-zonation of the Iberian Massif). The shear zone dips towards the S or SW, showing a top-to-the-S sense of movement. Early ductile deformation was concentrated along a band of andalusite-rich carbonaceous shales in the shear zone, but this can also be recognized in the footwall, particularly in the eastern sector, where the southern border of the (pre- to syn-kinematic) Santa Elena stock was intensely sheared; later intrusion of dyke-swarms agrees with the extensional stress field. Finally the shear zone appears brecchiated and bounded by two brittle faults. From a regional point of view, the shear zone described separates rocks with some differences regarding their stratigraphic, igneous and structural characteristics. These differences, and their precise limits, have been the basis for numerous subdivisions of this part of the Iberian Massif during the last decades. It is our contention that if any subzonation of the southern Central Iberian Zone is to be made (namely eg : Obejo-Valsequillo Domain, Lusitan-Marianic Domain), its northern boundary should be the Puente Génave-Castelo de Vide shear zone. As for the southern boundary, it is located in the Badajoz-Córdoba suture that separates the Central Iberian Zone from the Ossa-Morena Zone.