The microstructural features of Al 5754 friction stir spot welds are investigated using transmission electron microscopy (FEM) and electron back-scattered diffraction (EBSD). It is shown that EBSD misorientation maps using a 2 degrees misorientation criterion provide average subgrain dimensions which are very similar to those found using TEM microscopy. Average subgrain dimensions in the stir zone increased (from 2.92 mu m to 3.71 mu m) when the dwell time during spot welding increased from 1 s to 4 s. There was also no evidence of grain growth as the spot welds cooled following the joining operation.