Objective To explore the relationship between leg length discrepancy (LLD) and scoliosis in adolescent idiopathic scoliosis (AIS) patients, and to analyze the improvement of LLD after orthopaedic surgery and the risk factors. Methods The clinical data were collected from 85 AIS patients admitted to Department of Spine Surgery of Changhai Hospital, Naval Medical University (Second Military Medical University) from Jan. 2010 to Jan. 2013. The height difference of bilateral femoral head (HD-bFH) on standing X-ray images and the changes of HD-bFH after orthopaedic surgery were measured using the imaging data before operation and 2 years after operation. According to preoperative HD-bFH, the patients were divided into non-LLD group (HD-bFH<5 mm) and LLD group (HD-bFH ≥ 5 mm). The general characteristics and imaging parameters were compared between the two groups, and the correlation between HD-bFH changes and other parameters was analyzed. Results The HD-bFH of the 85 AIS patients was (0.80±5.57) mm before operation and (-0.49±4.93) mm 2 years after operation, and the difference was significant (P=0.022). There was no significant difference in HD-bFH between the patients with main thoracic curves (Lenke typeⅠ, Ⅱand Ⅲ; n=50) and thoracolumbar/lumbar curves (Lenke type Ⅴ and Ⅵ, n=33;[0.52±5.86] mm vs[1.53±5.12] mm, P=0.427). Among the 85 patients, 31 (36.5%) had LLD. There were no significant differences in general features and imaging parameters between the non-LLD group (n=54) and the LLD group (n=31, P>0.05). Postoperative change of HD-bFH was correlated with Risser sign (r_s=-0.512, P=0.020) and the orthopedic degree of lumbar curvature (r=-0.605, P=0.018). Conclusion The prevalence of LLD is 36.5% in AIS patients. Changes of leg length in AIS patients are closely related to orthopedic surgery, and the orthopedic degree of lumbar curvature and Risser sign are the risk factors.