PurposeWe aimed to develop and internally validate a scoring system, the adult spinal deformity surgical decision-making (ASD-SDM) score, to guide the decision-making process for ASD patients aged above 40 years.MethodsA multicentre prospective ASD database was retrospectively reviewed. The scoring system was developed using data from a derivation set and was internally validated in a validation set. The performance of the ASD-SDM score for predicting surgical management was assessed using the area under the receiver operating characteristic curve (AUC).ResultsA total of 702 patients were included for analysis in the present study. The scoring system developed based on 562 patients, ranging from 0 to 12 points, included five parameters: leg pain scored by the numerical rating scale; pain and self-image domains in the Scoliosis Research Society-22 score; coronal Cobb angle; and relative spinopelvic alignment. Surgical indication was graded as low (score 0 to 4), moderate (score 5 to 7), and high (score 8 to 12) groups. In the validation set of 140 patients, the AUC for predicting surgical management according to the ASD-SDM score was 0.797 (standard error=0.037, P<0.001, 95% confidence interval=0.714 to 0.861), and in the low, moderate, and high surgical indication groups, 23.7%, 43.5%, and 80.4% of the patients, respectively, were treated surgically.ConclusionsThe ASD-SDM score demonstrated reliability, with higher scores indicating a higher probability of surgery. This index could aid in the selection of surgery for ASD patients in clinical settings.