This study looks at the effect of laser welding on residual stresses in sheets of moulded magnesium alloy (AZ91). The modifications are significant even though they are localised along the weld line. The welding process produces a gradient of residual stresses from the weld line to the base metal and throughout the thickness of the weld zone. The distribution of these residual stresses has been qualitatively explained by the kinetics of cooling and by the nature of the multiphase material. Finally, it has been demonstrated that a pronounced crystallographic texture modifies local distribution of residual stresses. These results show that there is a complex coupling between the metallurgical, thermal and mechanical aspects generated by high power welding procedures.