Objectives : The arterial switch operation(ASO) has become the treatment of choice for repair of transposition of the great arteries(TGA). The outcome in terms of survival is excellent. However, neoaortic root dilatation(ARD) and neoaortic regurgitation(AR) is a major long term concern after ASO. The aim of this study was to evaluate the fate of the neoaortic valve function after ASO and to identify risk factors for this. Methods : Between April 1991 and July 2008, 239 patients had an ASO for TGA in our institution. Perioperative and follow up data on 216 hospital survivors were retrospectively reviewed. Results: Upon the time of discharge, grade I AR was present in 19(19/216, 8.7%) patients and grade II AR in 3(3/216,1.3%)patients. At the last follow-up (mean duration 78.83짹52.86 months), 31(31/216,14.3%) patients had a grade I AR and 6(6/216, 2.7%) patients had a grade II AR. None had a grade III or greater AR. The neoaortic valve was replaced only in 1 patient with both grade GII AR and LV dysfunction. Independent risk factors of grade II AR by multivariate analysis were the presence of AR at the time of discharge(p=0.04) and neoaortic sinus z-value(p=0.002). Z value of neoaortic sinus was greater than 3 in 45(45/216, 20.8%) patients at the last follow-up echocardiography. On multivariate analysis, Taussig-bing anomaly and PS were significantly associated with ARD. Freedom from grade II AR was 97.5% at 10 years. Conclusions : After the ASO, ARD and AR tended to increase over time. However, significant AR and the need for valve replacement for AR were rare. Taussig-bing anomaly and PS enhanced ARD. Neoaortic sinus dilatation and AR at the time of discharge were closely related to grade II AR.