The fatigue behavior of load-carrying cruciform fillet welded joints has been studied extensively using the dual boundary element method. This method, which incorporates two independent boundary integral equations, uses the displacement equation to model one of the crack boundaries and the traction equation to model the other. As a consequence, the analysis of the welded joints can be performed effectively in a single-region formulation. It is shown that the stress intensity factors (SIFs) at the weld toe and at the weld root are approximately equal when γ and λ are equal to 1.0 and 1.7, respectively, where γ and λ are the ratios of the embedded crack length 2a, and weld leg length w, to the main plate thickness T. In other words, the weld size, w, should be <1.7 times the main plate thickness in order for the crack to propagate from the weld root. Using these conditions, the magnification factor, Mk, and the SIFs, K, at the weld root, are calculated using the J-integral in the analysis. They are compared...