Purpose: Aortic Customize is a new concept for endovascular aortic aneurysm repair in which a non polymerized elastomer is injected to fill the aneurysm sac around a balloon catheter. The aim of this in vitro study was to investigate the extent of aneurysm wall stress reduction by the presence of a noncompliant elastomer cuff. Methods: A thin-walled latex aneurysm (inner radius sac 18 mm, inner radius neck 8 mm), equipped with 12 tantalum markers, was attached to an in vitro circulation model. Fluoroscopic roentgenographic stereo photogrammetric analysis (FRSA) was used to measure marker movement during six cardiac cycles. The radius of three circles drawn through the markers was measured before and after sac filling. Wall movement was measured at different systemic pressures. Wall stress was calculated from the measured radius (sigma = pr/2t). Results: The calculated wall stress was 7.5-15.6 N/cm(2) before sac filling and was diminished to 0.43-1.1 N/cm(2) after sac filling. Before sac filling, there was a clear increase (P <.001) in radius of the proximal (range, 7.9%-33.5%), middle (range, 3.3%-25.2%), and distal (range, 10.5%-184.3%) rings with increasing systemic pressure. After sac filling with the elastomer, there remained a small, significant (P <.001) increase in the radius of the circles (ranges: 6.8%-8.8%; 0.7%-1.1%; 5.3%-6.7%). The sac filling reduced the extent of radius increase. The treated aneurysm withstood systemic pressures up to 220/140 mm Hg without noticeable wall movement. After the sac filling, there was no pulsation visible in the aneurysm wall. Conclusions: Filling the aneurysm sac of a simplified in vitro latex model with a biocompatible elastomer leads to successful exclusion of the aneurysm sac from the circulation. Wall movement and calculated wall stress are diminished noticeably by the injection of biocompatible elastomer. (J Vase Surg 2010;51:1230-7.) Clinical Relevance: Filling the aneurysm sac with an elastomer has a lot of potential advantages, compared with the current endovascular treatment options. To fill the sac with the biocompatible elastomer, only a fill catheter with diameter of minimal 7 F and endovascular balloons need to be introduced transfemorally to the aneurysm sac. Most stent grafts need a minimal diameter of 14 F-22 F for access to the bulky delivery sheath, which makes many aneurysms with strong tortuosity or occlusive disease of the iliac arteries ineligible for treatment. In theory, any abdominal aortic aneurysm with a deviant anatomy will become treatable, as endovascular balloons will be available in different kinds of shape and configurations. As stated above, future research must take place before this treatment option can be applied in vivo. Animal experiments will take place to prevent embolic complications during the filling process and to investigate the short- and long-term effects of the presence of the elastomer its the aorta. Research on this novel treatment concept is in full progress and will be reported in the near future.