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BACKGROUND Zoster-related pain (ZRP) has many negative effects on a patient's quality of life. The transforaminal steroid injection (TFESI), which reduces neural inflammation and pain, has been advocated by pain physicians. Many reports demonstrated that early administration of TFESI showed better efficacy; however, the golden period during which TFESI is most effective remains unclear. OBJECTIVES This multicentre retrospective cohort study aimed to identify the golden period by which TFESI yields the best outcome in patients with ZRP. STUDY DESIGN Multicenter, retrospective cohort study. SETTING University-affiliated hospitals. METHODS After performing the TFESI in patients with ZRP, the patients were classified into two groups: the effective group (E) and the not effective group (N) based on the changes in the pain intensity 3 months after the TFESI. The receiver operating characteristic (ROC) curve analysis was used to assess the cut-off time point for predicting TFESI effectiveness. Furthermore, a logistic regression analysis was performed to identify patients' factors associated with a successful treatment outcome. RESULT Of the 302 patients, 186 and 116 patients were classified into the E and N group, respectively. ROC curve analysis showed that the best cut-off time point for TFESI was 12 weeks (95% confidence interval [CI]; 10-14 weeks) after the onset of HZ. The only variable associated with a favorable outcome was a symptom duration of ? 12 weeks compared with > 12 weeks (Odd ratio, 0.107; 95% CI, 0.055-0.205; P < 0.001). Other patient variables were not significantly associated with the effectiveness of TFESI. TFESI was most effective when administered within 12 weeks of the onset of herpes zoster. LIMITATION This study was not a prospective randomized controlled trial (RCT) and the follow-up period was only 3 months after TFESI. CONCLUSION TFESI is more effective when administered within 12 weeks of onset of herpes zoster.