Laser in situ fenestration (LISF) is emerging as an immediately available alternative in the endovascular treatment of complex aortic aneurysm. However, its biomechanical features remain poorly understood. The aim of this study was to experimentally evaluate textile damage secondary to LISF and to compare LISF with mechanical in situ fenestration (MISF).An in vitro study evaluated the damage created by LISF on endograft fabrics versus MISF using a needle. Five different models of commercially available aortic endografts were used (32 samples of polyethylene terephthalate and expanded polytetrafluoroethylene fabrics). Tensile strength tests were performed on the fabrics before and after in situ fenestration, to determine the loss of mechanical strength. Integral water permeability tests at the stent-fenestration interface evaluated the watertightness of junctions. Stability of the connection was assessed with a fatigue bench test flexing the branch on the fenestration. In a second step, an in vivo study evaluating LISF in sheep was conducted.Resulting holes had circular and cauterised edges following LISF, whereas fabric filaments were pushed aside after MISF. Tensile tests demonstrated a 34% and a 27% mechanical resistance loss after LISF (p = .004) and MISF (p = .001) compared with non-fenestrated samples. A non-significant global decrease of 7% in mechanical resistance was found following LISF compared with MISF (p = .520). Water permeability tests highlighted that leak rates were higher following LISF than with MISF with regard to multifilament specimens (p < .05). Fatigue tests induced modification of the morphology of fenestrations. The surface area of the fenestration was increased for all samples after 170,000 cycles. Regarding the in vivo study, 14 LISF were performed in 12 sheep with a technical success rate of 88%.This study demonstrates that both LISF and MISF create substantial damage to all available endograft fabrics. Until comparisons with reinforced fenestrations are performed, LISF and MISF should not be used outside investigational studies.