The role of porosity in 3D printed Acrylonitrile Butadiene Styrene (ABS) is studied. Dense samples are printed using fused deposition modelling with different orientations. X-ray m-tomography is used to reveal the 3D microstructures of the printed samples. Image analysis is applied to derive porosity content, connectivity and size distribution. Mechanical analysis is performed by converting 3D acquired images into finite element models. Simulation of uniaxial loading is carried out to predict the anisotropy induced by the printing process. Engineering constants including Poisson's coefficients and Young's moduli are derived. The results show that the low porosity content contrasts with high pore connectivity. Finite element computation reveals a slight transverse isotropy and weak sensitivity of the engineering constants with respect to sampling performed in both building and lateral directions. Comparison with experimental results indicates matching for Poisson's coefficients and higher sensitivity to printing orientation for Young's moduli. Sources of mismatching are attributed to interfacial effects where lack of inter-filament bonding is found to drive significantly filament decohesion perpendicular to the compression direction. (C) 2015 Elsevier Ltd. All rights reserved.