A structural field study of 750 fault planes has been carried out in order to understand the structural evolution of western Turkey. This analysis shows that the region has been affected during the Neogene period by successive, different trending, extensional events. A first, probably middle to late Miocene extensional phase that gave rise to NNE-SSW to NE-SW trending grabens was followed by a N-S extension, active from Lower Pliocene to Quaternary time. These Miocene and Pliocene extensions are probably related to the opening of the Aegean Sea. The direction of extension changed sometimes during the Quaternary from N-S to NE-SW. This younger episode of extension is still active in the region, as observed on active fault planes and as suggested by focal mechanisms of shallow earthquakes. In the northern part of the area, south and along the Edremit fault, this later extension is associated with a NW-SE compression attributed to the motion of the Anatolian plate along the northern Anatolian fault and its southern strands.