According to the reviewed studies, building orientation has a significant effect on the fatigue life of SLM steels, and horizontally built specimens have better mechanical properties over the vertical ones. These superior mechanical properties are dominantly achieved by the more modified thermal gradients, finer microstructure, and the appropriate direction of the linear and planar defects in horizontal specimens. However, thermal gradients and their consequent microstructural textures seem to be directly influenced by the aspect ratio rather than the building direction. Some of the current studies confused these two parameters and attributed the effects of the aspect ratio to the building direction. Thus, further research is required to study the aspect ratio as an independent process parameter to investigate its effects on the mechanical properties of SLM steels.