A pressure compensating device for a plasma display panel expands from an unextended position at lower altitudes to an expanded position at high altitudes to maintain the pressure differential across the panel sidewalls within predetermined limits. One embodiment includes a bellows assembly positioned on the rear wall of the plasma panel. The end wall of the bellows contacts an internal stop at lower altitudes so that the volume inside the bellows is as small as possible. As the pressure differential across the panel sidewall increases, either as a result of changes in the ambient temperature or pressure, the bellows moves in an axial direction to its extended position providing an additional volume in which the panel gas is received. Accordingly, the pressure differential across the panel sidewall can be maintained below a certain predetermined level irregardless of changes in ambient pressures and temperatures.