Abstract: A convertible motor vehicle with at least one seat having an extendable roll bar incorporated into an upper portion thereof. In one embodiment the roll bar forms part of the headrest of the seat in a retracted rest position and is automatically extended upward from the headrest into a locked, extended operating position. The extended roll bar cooperates with the reinforced framework of the backrest of the seat which is mounted to the vehicle chassis in the conventional manner to provide a sufficient structural member to support a vertically downward impact load on the extended roll bar that occurs when the vehicle rolls over. Known motion sensors are used to trigger the roll bar and cause a release from its rest position to its operating position. In an alternate embodiment of a seat without a headrest, the roll bar forms an upper portion of the backrest of the seat while in its rest position and extends upward into its operating position in the same manner as the headrest embodiment.