This study focuses on the fatigue resistance of aluminum friction-stir-welded (FSW) butt joints beyond the current design standards such as Eurocode 9 and CSA S6, which use generic S–N curves. A database of 1041 data points from 92 studies is analyzed using a statistical methodology by alloy, FSW variant, and stress ratio. The results show that fatigue strength more strongly depends on the alloy rather than on welding FSW variant. While existing codes give conservative estimation of the fatigue strength at a 50% probability of failure, they may be unconservative for lower probability of failure due to data scatter. This conclusion highlights the need for grade-specific S–N curves and additional guidance on scatter assessment.