STUDY DESIGN: Prospective, multicenter, international, observational study. OBJECTIVE: Identify independent prognostic factors associated with achieving the minimal clinically important difference (MCID) in patient reported outcome measures (PROMs) among adult spinal deformity (ASD) patients ≥60 years of age undergoing primary reconstructive surgery. METHODS: Patients ≥60 years undergoing primary spinal deformity surgery having ≥5 levels fused were recruited for this study. Three approaches were used to assess MCID: (1) absolute change:0.5 point increase in the SRS-22r sub-total score/0.18 point increase in the EQ-5D index; (2) relative change: 15% increase in the SRS-22r sub-total/EQ-5D index; (3) relative change with a cut-off in the outcome at baseline: similar to the relative change with an imposed baseline score of ≤3.2/0.7 for the SRS-22r/EQ-5D, respectively. RESULTS: 171 patients completed the SRS-22r and 170 patients completed the EQ-5D at baseline and at 2 years postoperative. Patients who reached MCID in the SRS-22r self-reported more pain and worse health at baseline in both approaches (1) and (2). Lower baseline PROMs ((1) - OR: .01 [.00-.12]; (2)- OR: .00 [.00-.07]) and number of severe adverse events (AEs) ((1) - OR: .48 [.28-.82]; (2)- OR: .39 [.23-.69]) were the only identified risk factors. Patients who reached MCID in the EQ-5D demonstrated similar characteristics regarding pain and health at baseline as the SRS-22r using approaches (1) and (2). Higher baseline ODI ((1) - OR: 1.05 [1.02-1.07]) and number of severe AEs (OR: .58 [.38-.89]) were identified as predictive variables. Patients who reached MCID in the SRS22r experienced worse health at baseline using approach (3). The number of AEs (OR: .44 [.25-.77]) and baseline PROMs (OR: .01 [.00-.22] were the only identified predictive factors. Patients who reached MCID in the EQ-5D experienced less AEs and a lower number of actions taken due to the occurrence of AEs using approach (3). The number of actions taken due to AEs (OR: .50 [.35-.73]) was found to be the only predictive variable factor. No surgical, clinical, or radiographic variables were identified as risk factors using either of the aforementioned approaches. CONCLUSION: In this large multicenter prospective cohort of elderly patients undergoing primary reconstructive surgery for ASD, baseline health status, AEs, and severity of AEs were predictive of reaching MCID. No clinical, radiological, or surgical parameters were identified as factors that can be prognostic for reaching MCID.