Widespread fatigue damage (WFD) is an important concern of aging aircrafts. Residual strength of stiffened panels with widespread fatigue damage was evaluated by an engineering approach and a finite element method respectively. Nine stiffened panels with three types of damage were tested for their residual strength. The predictions are in good agreement with the experiment results and it is shown the methods could be used in an engineering practice for the residual strength evaluation with the acceptable accuracy. It can be seen from this research that WFD could result in significantly reduction in the residual strength of stiffened panels.