Objectives/Hypothesis: We sought to characterize rates of progression to posterior glottic stenosis (PGS) from autoimmune or idiopathic subglottic stenosis. Study Design: This was a retrospective review. Methods: Patients from a tertiary-care laryngology practice over a 10-year period with autoimmune or idiopathic subglottic stenosis (SGS) were included. Patients with a history of prolonged intubation or other causes of iatrogenic stenosis were excluded. PGS was confirmed on videostrobolaryngoscopy recordings by a fellowship-trained laryngologist. PGS type (1–4) was also recorded. Demographic information was recorded, and if applicable, autoimmune disease type was specified. Time until PGS was recorded along with the number of interventions. Chi-squared analysis was used to compare PGS in autoimmune and idiopathic SGS. Results: A total of 77 patients were identified with autoimmune (32 patients) or idiopathic (45 patients) subglottic stenosis. Autoimmune pathologies included systemic lupus erythematosus, granulomatosis with polyangiitis (GPA), rheumatoid arthritis, relapsing polychondritis, and sarcoidosis, with GPA the most common (14/32). Patients with autoimmune SGS had a higher rate of PGS (10 of 32) compared to idiopathic subglottic stenosis (1 of 45) for an odds ratio of 20 (95% CI: 2.4–166.4, P =.006). Patients with idiopathic SGS were more likely to be female (all 45 compared to 29/32 autoimmune, P =.07) and older (mean 53 (range 29–75) compared to 46 (20–82), P =.02). Conclusions: In this large patient cohort, autoimmune SGS patients were found to have a higher likelihood of developing PGS compared to their idiopathic counterparts, suggesting that counseling for this progression may be warranted. Level of Evidence: 4 Laryngoscope, 131:1816–1820, 2021.