Experiments were conducted on an Al-0.6 % Mg-0.4 % Si alloy to evaluate the effect of different preliminary thermal treatments on the evolution of microstructure and microtexture during processing by High-Pressure Torsion (HPT). Disks of the alloy were solution-treated, then some disks were briefly aged at 473 K, and other disks were briefly aged at 523 K before processing by HPT for up to 20 complete revolutions. The processing by HPT refined the microstructure to an average grain size as small as similar to 0.25 mu m in the solution-treated alloy after 20 turns but preliminary aging led to slightly larger average grain sizes of similar to 0.35-0.40 mu m after 20 turns. For all processing conditions, there was a high fraction of high-angle grain boundaries after HPT and it is shown that aging introduces changes in the microtexture intensities.