Objective: The purpose of this study was to define changes in aneurysm volume after endovascular repair of abdominal aortic aneurysm. Methods: A total of 154 consecutive patients who underwent endovascular repair of abdominal aortic aneurysm with the Medtronic AneuRx stent graft at Stanford University Hospital were evaluated. During a mean follow-up period of 15.8 ± 11.3 months, serial computerized measurements of aneurysm volume and orthogonal maximal diameter were performed on helical computed tomographic scan data sets and maximal transverse diameter was measured manually from transverse computed tomographic images. Aortoiliac length (renal to hypogastric artery origin) was measured along the median luminal centerline and along the straight line. Results: Aneurysm volume increased immediately after endovascular repair (from 180.2 ± 69.9 mL to 187.9 ± 71.6 mL; P < .001), but orthogonal and transverse diameter and aortoiliac length did not change significantly. During the follow-up period, mean volume decreased to 171.9 ± 70.2 mL (P < .05) and straight-line and centerline aortoiliac length remained unchanged from preoperative values. Overall, volume decreased at a rate of 1.7 ± 5.9 mL/mo (P < .001). During periods without endoleak, the rate of decrease was 3.2 ± 5.5 mL/mo (P < .001), and during periods with endoleak, aneurysm volume increased at a rate of 2.0 ± 5.3 mL/mo (P < .005), without a difference between types of endoleak. Predictive values for the presence of endoleak were similar for transverse and orthogonal diameter and volume. Logistic regression analysis showed volume to be most closely associated with the presence of endoleak. Conclusion: Aneurysm volume increases immediately after endovascular repair. After repair, aneurysm volume gradually decreases and aortoiliac length remains unchanged. Changes in volume parallel changes in maximal aneurysm diameter, and their association with the presence of an endoleak does not appear to be appreciably stronger.