IMPORTANCE: Endoscopic dilation is the mainstay treatment strategy for subglottic and proximal tracheal stenosis (SGS/PTS). Its major limitation is restenosis requiring repeated surgery. Intralesional steroid injection (ISI) is a promising adjunctive treatment aimed at prolonging the effects of dilation. OBJECTIVE: To evaluate the association of serial in-office ISI after endoscopic dilation with surgery-free interval (SFI) in adults with SGS/PTS. DESIGN, SETTING, AND PARTICIPANTS: A retrospective study of adults with SGS/PTS who underwent at least 2 consecutive in-office ISI at the University of Southern California, Keck School of Medicine, over a 3-year period was conducted. EXPOSURE: Serial ISI with triamcinolone 40 mg/mL using topical anesthesia, spaced 3 to 6 weeks apart. MAIN OUTCOMESAND MEASURES: Surgery-free interval, number of dilations, need for open airway surgery, decannulation rate, and adverse events. Patients with previous dilations and sufficient follow-up time were included in a comparative analysis of SFI before and after ISI. The Mann-Whitney U test was applied for comparisons. RESULTS: Twenty-four patients met eligibility criteria. Mean (SD) age was 50.1 (15.1) years; 18 (75%) were female. Ten (42%) patients had idiopathic, 8 (33%) had traumatic, and 6 (25%) had rheumatologic-related SGS/PTS. Mean (SD) follow-up time was 32.3 (33.4) months. Patients underwent mean (SD) 4.08 (1.91) injections. Seventeen (71%) patients have not undergone further surgery after ISI. Mean (SD) SFI was 17.8 (12.8) months overall and was 15.7 (10.6) months for idiopathic, 13.8 (9.9) for traumatic, and 26.7 (16.9) for rheumatologic-related SGS/PTS. Twenty-one (88%) patients underwent dilation(s) prior to ISI. Among patients who fulfilled eligibility criteria for comparison of SFI before and after ISI, SFI improved from 10.1 months before, to 22.6 months after ISI (mean difference, 12.5 months; 95% CI, -2.1 to 27.2 months). Three of 6 patients (all with traumatic SGS/PTS) presenting with a tracheotomy were decannulated. No patients required open airway surgery after ISI. There were no adverse events associated with ISI. CONCLUSIONS AND RELEVANCE: Serial in-office ISI are safe and well-tolerated in adults with SGS/PTS. This technique can reduce the surgical burden on these patients and may obviate the need for future airway intervention.