As refill friction stir spot welding is seen as a potential successor to riveting and resistance spot welding in the automotive and aircraft industries, interest in the dynamic load-bearing capacity of welded joints is also growing. Since dynamic load-bearing capacity is strongly dependent on the residual stress state, this study investigated the effects of welding parameters on the residual stress distribution of refill friction stir spot welded joints. In addition to temperature and hardness, residual stresses were measured using X-ray diffraction. Among other aspects, it is shown that the absolute level of residual stresses within the spot weld does not depend on the welding parameters, but the area in which they act does.