Geological cross-section through the western border of the Basque-Cantabrian Basin shows the existence o f extensional faults active during Permo-Mesozoic sedimentation, as well as their tectonic inversion during Alpine deformation. An analysis of the tectonic inversion activity and related paleostress tensors has been carrried out using structural methods and fault population analysis. Two different paleostress tensors, extensional and compressive, have been deduced from fault-slip data. Compressive paleostress tensor has a horizontal and N-S trendings,St similar to paleostress data deduced from other alpine chains located in the northern Iberian peninsula