Posterior minimally invasive scoliosis surgery (MISS), utilizing 2 to 3 mini-open incisions, has demonstrated radiological outcomes comparable to conventional open surgery (COSS), while offering superior perioperative results and cosmetic satisfaction in moderate-to-severe adolescent idiopathic scoliosis (AIS). However, there is a paucity of literature regarding the feasibility of this technique for very severe curves exceeding 80°, which are traditionally considered difficult indications for MISS due to the complexity of deformity correction in the limited surgical vision. A total of 257 flexible AIS patients who underwent deformity correction using posterior MISS were retrospectively categorized into three groups based on the curve magnitude: moderate (M group, main Cobb angle < 60°, n = 142), severe (S group, 60°–80°, n = 91), and very severe (VS group, ≥ 80°, n = 24). Radiological parameters (Cobb angle, coronal balance, sagittal vertical axis, thoracic kyphosis, and lumbar lordosis), perioperative outcomes (fused segments, scar length, number of skin incision, thoracoplasty, hospital days, operative time, estimated blood loss, and blood transfusion) and complication (pleural effusion, pneumothorax, pneumonia, venous thromboembolism, scar revision, deep infection, abnormal intraoperative MEP signal, neurological deficit, metal failure) rates were compared among the three groups. The VS group required significantly longer operative times (P < 0.001), more fused segments (P < 0.001), and a greater number of rib resections during thoracoplasty (P = 0.032) compared to the other groups. Despite these surgical demands, there were no statistical differences in the correction rate (P = 0.954) and last follow-up thoracic kyphosis (P = 0.830) among the three groups. Regarding complications, while the overall complication rate showed no statistical difference, the VS group required significantly more invasive management for pleural effusions (P = 0.012). Therefore, posterior MISS demonstrated acceptable radiological and perioperative outcomes even in flexible AIS with Cobb angles > 80°. These findings support the feasibility of MISS as a viable surgical option in flexible and very severe cases, suggesting an expanded indication for its application in AIS.