OBJECTIVE To review the dilatation of the proximal neck in abdominal aortic aneurysm (AAA) after endovascular repair (EVR), and to analyze the factors contributed to these changes. METHODS From January 1997 to January 2007, a total of 45 patients treated by EVR met the inclusion criteria. There were 44 male and 1 female patients, with an average age of (69 ± 17) years. The patients were all asymptomatic abdominal aortic aneurysm, combined hypertension in 37 cases, coronary heart disease in 40 cases. All the patients had the complete preoperative enhanced CT information, and accepted more than 6 months of regular enhanced CT follow-up (1, 3, 6, 12 months after surgery and annually thereafter). The proximal aneurysm neck diameter increase was determined by CT, increase over 2 mm as having change, less than 2 mm as no change. RESULTS The average follow-up interval was (34 ± 25) months (ranging from 9 to 100 months). The mean preoperative proximal neck diameter was (21.5 ± 2.3) mm, and (22.4 ± 2.4) mm one month after operation and (24.0 ± 2.8) mm at the latest follow-up. The increase of proximal neck diameter was detected in 71.1%. The oversizing percentage was 19% ± 6%. The incidence of proximal neck over-sizing stent-graft in diameter was 6.7%. The incidence of no dilation at proximal neck diameter was 97.4%, 68.6%, 39.3% and 3.3% at 16, 24, 36 and 96 months postoperatively respectively. The stent-graft migration was detected in 22.2% patients, and the migration distance was (7.0 ± 1.3) mm (ranging from 0 to 9.5 mm). There were no case which the migration oversized 10 mm or need to reintervention. CONCLUSIONS The more oversizing percentage, the more dilatation in the proximal neck. The stent-graft migration and the dilatation of the proximal neck might have effect on each other.