Background Marfan syndrome (MFS) leads to aortic root aneurysm, while descending thoracic aortic aneurysm (TAA) occurs less commonly. Abdominal aortic aneurysm (AAA) is rarely reported in MFS. Risk factors for AAA are poorly understood and there are no guidelines for AAA screening in MFS. We sought to characterize AAA among Marfan patients in our center. Methods The records of 12 adults with MFS and AAA disease were reviewed. Clinical features, imaging, operative reports, and outcomes were analyzed. Results Twelve adults with MFS and AAA were studied; age at AAA diagnosis was 44 ± 15 years (range 18–63). Nine patients smoked cigarettes. Eleven patients underwent prior aortic root replacement at age 31 ± 15 years. The size of AAA was 5.0 ± 1.3 cm (range 3.5–7.5) at the time of diagnosis. The AAA was suprarenal in 5, juxtarenal in 2, and infrarenal in 5 patients. Two patients had a descending TAA. Branch vessel aneurysms were present in 7 patients. Five patients underwent open surgical repair, 5 underwent endovascular repair, and 5 are being treated medically. One patient died suddenly with AAA size 5.7 cm, 2 months before death. Three patients subsequently developed type B aortic dissection, from 3 months to 9 years after AAA diagnosis. Conclusions Adults with MFS are at risk for developing AAA. Evaluation for AAA is recommended in adults with MFS and prior root replacement, especially if descending aortic or branch vessel aneurysm is present or the patient smokes cigarettes.