Introduction Robust wall apposition for flow-diverter stents (FDS) may be important for endothelialization. Using a large series of experimental aneurysms treated with the Pipeline Embolization Device (PED), the objectives of this study were to 1) assess interobserver agreement for the evaluation of wall apposition on post-treatment DSA and evaluate its association with aneurysm occlusion and 2) measure the relationship between wall apposition assessed with histology and aneurysm occlusion rate after PED treatment. Material and methods Saccular aneurysms were created in 41 rabbits and treated with PED. DSA was performed just after the deployment of the device and at follow-up. Three investigators independently graded wall apposition on post-treatment DSA as good or poor. One histopathologist blinded to the angiographic results, graded the wall-apposition on histological samples. We examined the correlation between angiographic occlusion and wall apposition with histology and angiography. Results Wall apposition evaluated on histology was strongly associated with saccular aneurysm occlusion. Sensitivity and specificity of wall apposition to predict complete occlusion at follow-up were, respectively, 76.9% and 84.0% with an overall accuracy 81.6%. In this experimental study, DSA was sub-optimal to assess flow diverter apposition with moderate inter-observer agreement and low accuracy. Conclusion Good wall apposition is strongly associated with complete occlusion following flow-diverter therapy. In this study, DSA is suboptimal for assessing wall apposition of FDS. These findings suggest that improved tools for assessing FDS wall apposition are highly relevant.