A new approach for risk evaluation of abdominal aortic aneurysm is based on wall stress distribution and determination of peak wall stresses using the finite element method. To clarify the influence of different model assumptions on results a study with models of different complexities is performed. Patient specific AAAs are modeled using 6 different approaches which are distinguished by linear or nonlinear material law, inclusion of thrombus and calcification, application of blood pressure load and prestressing technique. Deformations and peak wall stresses change remarkably between the different complexity grades. In most cases, simplifications lead to unrealistically increased displacements and stresses.