Al-0.1 Mg with a 3 mu m grain size was deformed in channel die plane strain compression at temperatures up to 200 degrees C. It was found that the reduction in grain thickness was significantly less than that predicted from geometric considerations, and at larger strains, a minimum high angle grain spacing, which was equal to the crystallite size was achieved. The velocity of the high angle boundaries during this process is very many orders of magnitude larger than that predicted for curvature driven grain growth, and some possible explanations for this are discussed.