A tailgate for a vehicle with side walls and a bed has a supplemental tailgate that retracts within a tailgate frame and is extendable therefrom. The supplemental tailgate may include a guide system secured generally between the rear panel and the front panel of the tailgate frame, a movable frame assembly having two telescoping supports extendable from, pivotable relative to and retained by the guide system. The supplemental tailgate may also include a cross member connected to the two telescoping supports and extending therebetween. A lock rod assembly telescopically extends from and is pivotable relative to the cross member, with the lock rod assembly including a lock rod bar having a lock rod latch affixed thereto that is adapted to releasably latch to one of the vehicle side walls to thereby support the movable frame portion relative to the guide system when the tailgate frame is in the generally horizontal open position and the movable frame assembly is pivoted upward relative to the tailgate frame.