Al films deposited on Pt layers developed voids after annealing between 200 and 300 °C. Void formation in the Al was also observed when the Pt layer was deposited above the Al film. The amount of Al surrounding the voids increased as the voids grew. The void growth seems to saturate when all the Pt is consumed to form Pt2Al3, and the rate of void growth decreases as the thickness of the initial Al film increases. We believe the controlling mechanism is diffusion along the Al/Pt interface made possible by compound formation there.