Friction stir welding (FSW) is emerging as a promising choice for joining high strength aluminum alloys. In this work, results of a study conducted on fatigue crack propagation in friction stir welded AA2050 and the effects of FSW induced residual stresses are presented. Longitudinal residual stress profiles across butt welded 2050 plates were determined using the cut compliance technique and fatigue crack growth testing was conducted on compact tension specimens machined from the friction stir welds. Tests were performed with the crack propagating nominally perpendicular to the weld and with a constant, applied, cyclic, stress intensity factor. Different cases were investigated, included different specimen configurations and material tempers, but in all cases residual stresses were found to have a major effect on the fatigue crack propagation. It was shown that compressive residual stresses are present in the vicinity of the weld and that these residual stresses lead to a decrease in the fatigue crack growth rate as the crack approaches the weld. Once in the weld nugget, the crack propagation rate increases again. The principal variations of fatigue crack growth rates in the different zones of the weld can be linked to the presence of residual stresses; however, microstructural effects were also noted.  Prediction of fatigue crack growth rates was attempted using both the residual stress intensity from the cut compliance testing and the measured ΔK_eff.