A mathematical model was developed to correlate the amplitude of the pillowing deformation of lap joints to the degree of corrosion inside the joint. Based on mathematical model, finite element techniques were used to determine the effect of pillowing in the stress in fuselage lap joints. The stress caused by the internal pressure and riveting process was taken into account, and the fuselage curvature was ignored. The results show that pillowing can significantly increase the stress in a lap joint for material loss below the detection limit of current nondestructive inspection techniques, thus increasing the risk of premature cracking. In addition, the analyses show that pillowing resulted in a stress gradient through the skin thickness, which suggest that semi-elliptical cracks with a high aspect ratio can form. In the last, the stress correction curves at the critical rivet hole were used in the AFGROW crack growth rate program to predict the residual life of corroded lap joint and the analytical results were close to available test date.