The aim of this work is to deliver a precise statement about the mechanical effect of microstructural defects induced by stereolithography. Design of cellular structures based on a photosensitive resin with varied porosity content is performed up to 60%. The compressive behaviour of these structures is captured and microstructural defects are analysed using X-ray micro-tomography. Finite element computation is considered to predict the compressive behaviour of both 3D microstructures and CAD (Computer-Aided Design) models up to the densification stage. X-ray micro-tomography analyses reveals that two main defects are generated by the process, namely residual support material and excess of resin trapped inside the porous network. Significance of the defects is proved to be related to the design of cellular structures with porosity levels in the range 10-30%. In addition, both experimental and numerical results show no evidence of anisotropic effect related to additive layering of resin. Finally, the suggested damage densification constitutive law captures the main characteristics of the compressive response of studied cellular structures.