This security door construction is applicable to safes, factory doors and house doors. An offset hinge assembly allows the door to swing open and closed and also to slide in and out of a door slot in the door frame at the closing edge of the door. In the construction of a safe, hooks on the inside of the door enter slots in upstands inside the safe and engage and disengage through the sliding motion. House doors and screen doors use a hinge assembly which operates in the same way as the safe. One pair of hinges are fixed to the frame and the second pair of hinges are fixed to the door. The frame and door pairs are connected by a rod or tube which ensures that the hinge axis of the door pair remains parallel to the hinge axis of the frame pair. A door locking mechanism is actuated by a conventional pneumatic door closer. A gas strut supplies the thrust to cause the mechanism to slide the door into the door slot when the door closer brings the door into register with the door slot.