Background Although previous reports had reported the use of temporary internal distraction as an aid to correct severe scoliosis,two-stage surgery strategy (less invasive internal distraction followed by posterior correction and instrumentation) has never been reported in the treatment of patients with severe spinal deformity.This study aimed to report the results of the surgical treatment of severe scoliosis and kyphoscoliosis by two-stage and analyse the safety and efficacy of this surgical strategy in the treatment of severe spinal deformities.Methods A total of 15 patients with severe scoliosis,kyphoscoliosis or kyphosis who underwent two-stage surgeries (less invasive internal distraction followed by posterior correction and instrumentation) were studied based on hospital records.Pretreatment radiographs and radiographs taken after first surgery (internal distraction by two small incisions),before second surgery (posterior correction,instrumentation and fusion),one week after second surgery and final follow-up were measured.Subjects were analyzed by age,gender,major coronal curve magnitude,flexibility of major curve,major sagittal curve magnitude before first surgery,after first surgery,before second surgery,after second surgery and at final follow-up.Complications related to two-stage surgeries were noted in each case.Results The average major curve magnitude was 129.4° (range,95° to 175°),reduced 58.9° or 45.4％ after first stage surgery and reduced 30.6° or 24.6％ after second stage surgery.The loss of correction during the interval between two surgeries was 7.1％.The total major coronal curve correction was 81.4°or 62.9％.At the final follow up,the average loss of correction of major coronal curve was 3.9° and the final average correction rate was 59.7％.The average major sagittal curve magnitude was 80.3° (range,30° to 170°),and the total major sagittal curve correction was 48.2°.Loss of correction averaged 4.0° for major sagittal curve and the final correction averaged 42.2°.Clinical complications were noted in the peri-operative and long-term periods.Conclusions Two-stage surgery was a safe and effective surgical strategy in this difficult population.Using two-small-incision technique,the first stage surgery was less invasive.No permanent neurologic deficit was noted in this series.