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Recently, the fatigue behavior of cast Al-Si alloys have been extensivelystudied for the increasing practical relevance. The fatigue behavior of these Al-alloysdepends on a number of mechanical and microstructural factors, in particular oncasting porosity. The present work is aimed at identifying a strategy for determining theactual impact of porosity on the fatigue response of a cast part, considering that adegree of porosity is inevitable for a standard casting process. Fatigue experimentshave been carried out on a cast AlSi7Mg alloy, (equivalent to A356), subjected to astandard T6 heat treatment. Light microscopy was used to characterize the materialmicrostructures and porosity. Casting pores were then considered as micro stressconcentrators and the influence of their shape, exactly reproduced from micrographs,on Kt determined by a linear elastic finite element analysis (FEA). Equivalent notchgeometries were then considered and the influence of notch plasticity verified by elastoplastic FEA.