Approximately ¼ of patients with thoracic aortic aneurysms (TAAs) have concomitant abdominal aortic aneurysms (AAAs), thereby justifying the addition of an abdominal CT scan to a chest CT scan in patients with a newly diagnosed or suspected TAA. However, the prevalence of pelvic artery aneurysms (PAAs) in these patients is unknown. The purpose of this study was to determine the prevalence of PAAs in patients with TAAs and to assess what patient specific factors were associated with PAAs, thereby providing insight into the usefulness of pelvic imaging in TAA patients. Consecutive non-operated patients seen in Cardiac Surgery clinic between 2008 and 2013 with a TAA and a CT scan of the chest/abdomen/pelvis were included. Scans of 371 patients were evaluated for PAAs using threshold diameters of 20 and 15 mm for common iliac artery aneurysms (CIAs) and internal iliac artery aneurysms (IIAs), respectively, on 3D analysis. The prevalence of PAAs was determined and multiple logistic regression was used to identify associated risk factors. 41 of 371 (11.1%) patients with a TAA had at least one PAA. Factors showing positive associations with PAAs included increased age (p = 0.0004), male gender (p = 0.0007), descending TAA location (p = 0.0024) and presence of an AAA (p < 0.0001). The results of our study suggest that the addition of pelvic imaging for PAA screening in patients undergoing an initial CT scan of the chest and abdomen for a TAA is valuable, particularly in patients with the following demographics: age ≥65, male gender, descending TAA location, and/or known AAA.