This paper describes an interactive, integrated system for damage tolerance design of aircraft stiffened panels. The tasks supported by the system range from the initial definition of the stiffened panel configuration to the elaboration of the residual strength and crack growth diagrams, including the mesh design and the incremental crack extension analysis. The structural configuration is represented in an object oriented fashion, using a high level of abstraction and in terms of object components well-known to the designer, such as stiffeners, cracks and boundaries. Input data is performed interactively, through a user-friendly windows-based interface and the boundary element meshes are automatically designed using a rule-based strategy. Crack propagation analysis is performed with the dual boundary element method which allows for the solution of problems involving single or multiple cracks under mixed mode conditions.