It is well-known that the fatigue behavior of cast aluminum alloy parts is largely determined by internal defects, particularly pores and inclusions. In this work, it is shown that such imperfections are also present in AlSi10Mg parts produced by selective laser melting, and serve as sites to initiate fatigue cracks. The effect of hatch spacing and building orientation on tensile and fatigue properties was tested. Oxide-driven pores dominate the fatigue resistance of the samples in this work. The larger oxide particles which are associated with crack initiation likely form by oxidation of metal vapor during part manufacture.