Defects in the bulk adhesive have been shown to reduce adhesive joins strength, which, in this paper, assumes an interfacial-type failure. Analysis indicates that voids (gaps) or disbond-type flaws in the adhesive will increase the peak stresses which occur at the joint ends and near the flaw itself. In this work, the shear stresses in the adhesive and the loads in the adherends are obtained for a single lap joint where the adhesive is assumed to undergo elastic-perfectly plastic behavior. Using a shear lag model, the adhesive is divided into yielded, elastic, and void (gap) regions and appropriate continuity conditions are utilized. Two non-dimensional parameters are identified and involve the overlap length of the joint together with the material and geometrical properties of the adherends and the adhesive. It is shown how the stresses are completely characterized by these parameters. The post-yield response is determined by calculating the ratio P-0/P-0L, where P-0 is the current non-dimensional post-yield load and P-0L is the corresponding load which starts adhesive yielding. This ratio is shown to be sensitive to a parameter, theta, which contains both geometrical and material properties. It is clearly indicated how values of this parameter and void size influence the post-yield load-carrying capacity of the joint, and how it can be a valuable parameter in design.