Reinforced hollow for a wind turbine tower comprising a lower ring (2) that determines an opening (3) for the installation of an access door (not represented) inside the tower (1). The hollow incorporates at least one structural element (4) that is fastened on both sides of the opening (3) of the tower's lower ring (2), providing the rigidness necessary to attach a door and permit the reduction of the thickness of the ring by 10-20%.