Abstract: A pre-assembled elevator shaft door assembly is installed in a shaft door opening equipped with a dowel plate, a carrier bracket and a pair of fastening plates. A protruding threshold carrier plate is mounted on the underside of the shaft door assembly and includes recesses which detent with a cut-out in the door carrier bracket. A pair of locking bar mechanisms are mounted at the upper corners of the door assembly for engaging locking bar pockets on the fastening plates to retain the shaft door assembly. Laterally extendable covering brackets on the door assembly are engaged by tongues on the fastening plates to bridge over the vertical air gaps. During the entire assembly time, the shaft door opening is secured by a movable barrier against the falling-in of persons.