Abstract： Objective To investigate the curve patterns and radiographic characteristics in male adolescents with idiopathic scoliosis (AIS) with Cobb angle more than 40°.Methods The medical records and preoperative radiographs of patients who had surgery for treatment of AIS between 2008and 2009,without any previous treatment for scoliosis,were retrospectively analyzed.The curve severity,flexibility,and thoracic kyphosis were analyzed on standing posteroanterior and lateral radiographs and side bending films.In addition,scoliosis curves were classified as typical or atypical in patterns and features for patient sub-group comparisons.Results 91 male and 260 female AIS patients were retrieved and both showed similar skeletal maturity.Atypical curves were more frequently observed in male patients (20.9％) than in female (10.0％) (P＜0.01).In patients with typical curve patterns,no gender difference was found in the distribution of atypical features.Males showed significantly higher incidence of major right thoracic curve,and greater frequency of hyperkyphosis than female patients.In patients who had typical curve patterns that included a major thoracic curve (single thoracic or double major curve patterns),male patients had larger magnitude of thoracic curve,more severe thoracic kyphosis,and more rigid thoracic and lumbar curves compared to female patients.Conclusions There are radiographic differences in the curve patterns,severity of scoliosis and kyphosis,and spinal flexibility between female and male AIS patients with Cobb angle more than 40.Atypical curve patterns were more predominant in male patients.In patients with typical curve patterns,the thoracic curve in male AIS might have higher risk of progression than that in female.The higher rigidity of both thoracic and lumbar curves in male AIS might contribute to the lower curve correction rate.In addition,male AIS patients with increased thoracic kyphosis may not have increased incidence of abnormal neural axis than in female.