BACKGROUND: Little is known of how frailty, a dynamic measure of physiological age, progresses relative to age or disability status. Operative treatment of adult spinal deformity (ASD) may play a role in frailty remediation and maintenance. PURPOSE: Compare frailty status, severe frailty development, and factors influencing severe frailty development among ASD patients undergoing operative or nonoperative treatment. DESIGN: Retrospective review with maximum follow-up of 3 years. SETTING: Prospective, multicenter, ASD database. PARTICIPANTS: Patients were consecutively enrolled from 13 participating centers. INCLUSION CRITERIA: ≥18 years undergoing either operative or nonoperative treatment for ASD, exclusion criteria: spinal deformity of neuromuscular etiology, presence of active infection, or malignancy. The mean age of the participants analyzed were 54.9 for the operative cohort and 55.0 for the nonoperative cohort. OUTCOMES MEASURES: Frailty status, severe frailty development, and factors influencing severe frailty development. METHODS: ASD patients (coronal scoliosis ≥20°, sagittal vertical axis (SVA) ≥5 cm, Pelvic Tilt (PT) ≥25°, or thoracic kyphosis ≥60°) >18 y/o, with Base Line (BL) frailty scores were included. Frailty was scored from 0 to 1 (not frail: <0.3, frail 0.3-0.5, severe frailty >0.5) through the use of ASD-frailty index (FI) which has been validated using the International Spine Study Group (ISSG) ASD database, European Spine Study Group ASD database, and the Scoli-RISK-1 Patient Database. The ISSG is funded through research grants from DePuy Synthes and individual donations and supported the current work. Operative (Op) and Nonoperative (Non-Op) patients were propensity matched. T-tests compared frailty among treatment groups and BL, 1, 2, and ≥3 years. An actuarial Kaplan-Meier survivorship analysis with log-rank (Mantel-Cox) test, adjusting for patients lost to follow-up, determined probability of severe frailty development. Multivariate Cox Regressions gauged the effect of sagittal malalignment, patient and surgical details on severe frailty development. RESULTS: The analysis includes 472 patients (236 Op, 236 Non-Op) selected by propensity score matching from a cohort of 1,172. Demographics and comorbidities were similar between groups (p>.05). Op exhibited decreased frailty at all follow-up intervals compared with BL (BL: 0.22 vs Y1: 0.18; Y2: 0.16; Y3: 0.15, all p<.001). Non-Op displayed similar frailty from BL to 2Y follow up, and increased frailty at 3Y follow up (0.23 vs 0.25, p=.014). Compared with Non-Op, Op had lower frailty at 1Y (0.18 vs 0.24), 2Y (0.16 vs 0.23), and 3Y (0.15 vs 0.25; all p<.001). Cumulative probability of maintaining nonsevere frailty was (Op: 97.7%, Non-Op: 94.5%) at 1Y, (Op: 95.1%, Non-Op: 90.4%) at 2Y, and (Op: 95.1%, Non-Op: 89.1%) at ≥3Y, (p=.018). Among all patients, baseline depression (hazard ratio: 2.688[1.172-6.167], p=.020), Numeric Rating Scale (NRS) back pain scores (HR: 1.247[1.012-1.537], p=.039), and nonoperative treatment (HR: 2.785[1.167-6.659], p=.021) predicted severe frailty development with having a HR>1.0 and p value<.05. Among operative patients, 6-week postoperative residual SVA malalignment (SRS-Schwab SVA+modifier) (HR: 15.034[1.922-116.940], p=.010) predicted severe frailty development indicated by having a HR>1.0 and p value <.05. CONCLUSIONS: Non-Op patients were more likely to develop severe frailty, and at a quicker rate. Baseline depression, increased NRS back pain scores, nonoperative treatment, and postoperative sagittal malalignment at 6-week follow-up significantly predicted severe frailty development. Operative intervention and postoperative sagittal balance appear to play significant roles in frailty remediation and maintenance in ASD patients. Frailty is one factor, in a multifactorial conservation, that may be considered when determining operative or nonoperative values for ASD patients. Operating before the onset of severe frailty, may result in a lower complication risk and better long-term clinical outcomes.