Background: Management of small AAAs (4.0 5.5cm) is a grey area in clinical practice. Two randomized controlled trials (RCTs) the United Kingdom Small Aneurysm Trial (UKSAT) and the Aneurysm Detection and Management Trial (ADAM) in the United States attempted to address the question, comparing immediate open surgical repair to surveillance and selective surgery. Neither trial showed improved survival with either treatment but revealed possible survival differences for patients within some AAA size and age subgroups. Likewise neither trial had adequate statistical power to evaluate differences within subgroups. Methods: We will investigate the treatment-survival associationwithin AAA size and age subgroups using the pooled UKSAT and ADAM patient-level data. A propensity-adjusted Cox model will be developed to assess the associations of interest. Results: Analysis of the table-based currently available showed that subgroup-specific survival treatment differences may be statistically significant after pooling data from the two trials we recently received the final datasets from the ADAM and UKSAT trials and results from the patient-level meta-analysis will be available to be presented at the Colloquium. Conclusions/Significance: This study will provide immediate information to discern patients with small AAAs for whom selective surveillance is the best treatment option from those who will benefit more from immediate surgery, facilitating development of improved treatment guidelines based on AAA size and patient age. Although endovascular repair for AAA has shown no long-term benefits over open surgery for AAAs>5.5cm, potential benefits for small AAA are still being investigated. Two RCTs (PIVOTAL/CAESER) are comparing endovascular repair and selective surveillance for small AAA neither trial individually has the statistical power to mirror this study subgroup analyses. Results from our research are critical for improving small AAA management and will be instrumental in designing future research and treatment guidelines.