Additive Manufacturing (AM) is a cutting-edge technology that allows the fabrication of mechanical parts characterized by very complex geometries providing also good mechanical properties to the final product. However, when the component to be produced is small-sized and high-detailed AM still presents some limitations. In particular, lattice structures produced by AM show dimensional inaccuracies respect to the designed CAD model, so the component is compromised also from a structural point of view. Thus, there is a substantial discrepancy between the mechanical properties of the designed lattice structure and the fabricated one. In an accurate design process this difference cannot be neglected: this paper explores which are the most common defects introduced by AM and how they affect mechanical behavior.