ObjectiveTo investigate the role of amygdala volume index(AVI) in surgcial evaluation in patients with mesial temporal lobe epilepsy (mTLE), including clinical features, etiologies and surgical outcome. MethodsThirty six patients were diagnosed as mTLE after surgical evaluation including clinical manifestations, video-electroencephalogram (VEEG) and magnetic resonance imaging (MRI) at the Second Affiliated Hospital of Zhejiang University between March 2013 and March 2016. Bilateral amygdala AVI was then calculated from amygdala volumes on MRI, which were measured with region of interest (ROI) analysis. All patients were treated surgically. Etiologies of mTLE were further confirmed by the histopathology of the resected tissue. ResultsAmong the 35 patients, there is a strong correlation between AVI on the lesion side and age of onset (R =-0.389, P = 0.019) as well as age of surgery (R =-0.357, P = 0.032). No obvious relation can be seen between AVI and gender, history of febrile convulsion, duration of epilepsy, secondary generalized seizure, side of lesion, presurgical seizure frequency and electrode implantation. There is no significant difference in AVI among the five etiologies. At follow-up, thirty patients (80.5%) reached seizure-free, AVI on the lesion side is nota predictor of surgical failure (P > 0.05). ConclusionAVI plays a role in etiology evaluation in patients with mesial temporal lobe epilepsy. Moreover, a larger AVI on the lesion side is correlated with an earlier age of onset. There is limited value of amygdala volume insurgical outcome prediction of patients with mTLE.