A deadbolt mechanism including a lock out mechanism that functions to disable the operation of the deadbolt from at least one side of the deadbolt mechanism. The deadbolt mechanism includes a deadbolt, key cylinder, housing, turn knob and a shaft that connects the key cylinder and turn knob. To place the deadbolt mechanism in lock out mode, a release mechanism is actuated and the turn knob is pulled outward away from the door. By pulling the knob outward, the shaft engages a portion of the housing which prevents rotation of the shaft and thereby prevents movement of the deadbolt from the lock-out position.