To ascertain whether preoperative symptom duration elevated the risk of adverse patient-reported outcomes (PROs) and to further delve into whether the existence of a dose-response relationship in patients with adult spinal deformity (ASD).The retrospective cohort comprised consecutive patients who underwent spinal corrective surgery from January 2018 to May 2022. Demographic, radiological and surgical factors were included from the electronic medical records. To identify the impact of mismatched variables, we performed conditional logistic regression after adjusting for potential confounding factors. Further, nonlinear relationship between symptom duration and postoperative unfavorable PROs at 24-month follow-up was conducted based on restricted cubic splines (RCS) analysis, with the adjustments for possible confounders. If a nonlinear relationship was identified, a two-piecewise regression model would be employed to ascertain the threshold effect. Finally, the result of receiver operating characteristic (ROC) curve was employed to further corroborated the rationality of RCS results.We matched 122 controls to 61 unfavorable PROs patients. In the fully adjusted linear model, for every additional month of symptom duration, the risk of unfavorable patient-reported outcomes (u-PROs) increased by 79%, with an odds ratio of 1.79 (95% CI: 1.25-2.04, p < 0.001). Patients with 6-18 months of symptom duration had comparable risk of u-PRO, whereas patients with more than 24 months had an increasingly higher risk of u-PRO (OR = 4.74, 95% CI 3.11 - 7.93, p < 0.001). Based on the results of the restricted cubic spline (RCS) analysis with three knots, a significant nonlinear relationship was observed. Notably, we found a substantial increase in the risk of u-PROs when the duration of symptoms exceeded 18.4 months. Additionally, ROC curve with an optimal cut-off of 18.5 months was identified, which verified the reliability of RCS analysis.We determine that 18.4 months was a threshold of preoperative symptom duration that shifted the risk of unfavorable PROs after spinal corrective surgery, and there was a dose-response relationship.© 2025. The Author(s).