Shot-peening is used extensively in the aerospace industry to generate compressive inplane near-surface residual stress fields to inhibit fatigue crack propagation from surface defects. The stress fields that are generated depend upon the material, the type of shot and the peening parameters which can be varied to optimise the residual stress field, principally to increase the compressive stress and the depth of the compressive layer. To determine the profile of the relatively steep stress field it is necessary to use a measurement technique that is capable of high spatial resolution. Traditionally X-rays with wavelengths of around 1.5 Angstrom, have been employed in near-hack-reflection to measure the residual stress in a surface layer a few microns thick. The surface is then repeatedly eroded to expose sub-surface layers so that the stress variation with depth can be measured. At the shorter wavelengths available at synchrotron sources the X-ray attenuation coefficients of light element materials are sufficiently small to permit internal residual strain fields to be mapped non-destructively. Results are presented of a synchrotron strain scanning investigation of samples of an aluminium alloy, hiduminium, that had been peened to four different intensities. The measurements were made, at the SRS, Daresbury, UK, using instrument 16.3 in its strain scanning mode with a wavelength 0.4 Angstrom and nominal gauge width 0.1 mm. The results compare well with results from traditional X-ray and hole drilling measurements on similarly peened samples. In the peening intensity range studied the surface residual stresses reach an approximately constant value above a certain peening intensity but the depth of the compressive layer increases with intensity. It is in principle possible to improve the spatial resolution when synchrotron strain scanning simply by decreasing the gauge size but there is a practical limit which is set by the grain size of the material. Coarse grained materials produce data of poor statistical quality. In the samples investigated it was found that peening reduced the grain size and the statistical data quality improved with peening intensity.