A vehicle door is reinforced by an integral reinforcement panel that is fixed to and reinforces side portions of an inner door panel. The reinforcement panel has an outer periphery adjacent and preferably abutting the outer door panel and includes stiffening flutes. Preferably, abutting portions of the outer panel and the stiffening panel are bonded together to form reinforcing box sections. Alternatively, a support panel may abut inner surfaces of the reinforcement panel and is preferably bonded to valley portions of the stiffening flutes to form the reinforcing box sections. The reinforcement panel may replace an anti-intrusion beam and other components of a conventional vehicle door.