Several N-S trending folds have been identified in the Eocene strata of the western Pyrenees. Stratigraphical and sedimentological lines of evidence show that they formed from late Ypresian to middle Lutetian times. These new data agree with previous works considering this time interval as a period of increasing tectonic activity. The N-S orientation of the folds is anomalous in the the pyrenean domain, where most tectonic structures are SE-NW elongated. Therefore, the N-S folds might have formed in response to local strains. They could represent «en echelon» folds related to the shear-stress produced by the dextral movement along the SW-NE trending Pamplona fault