STUDY DESIGN: Cross sectional OBJECTIVES: The purpose of this study is to evaluate the association between thoracic height and health-related quality of life (HRQoL) at skeletal maturity in patients with EOS. Current literature suggests a minimum thoracic height of 18 cm to 22 cm to avoid poor pulmonary function and related health outcomes. METHODS: Patients with EOS who reached skeletal maturity from 2005 to 2018 were identified in two registries including 32 centers. Thoracic height from T1 to T12 at skeletal maturity and Early Onset Scoliosis 24 Item Questionnaire (EOSQ-24) scores were collected. The EOSQ-24 domains included HRQoL of patients, parental impact, financial impact and patient and parental satisfaction. RESULTS: 469 patients (mean age: 14.9, female: 77.4%) were identified. 29% patients were of congenital etiology, 20.3% neuromuscular, 13.6% syndromic, 34.8% idiopathic, and 2.3% other. When patients were grouped by thoracic height at skeletal maturity, all EOSQ-24 domains increased after a threshold of 18 cm. When stratified by etiology, the 18 cm cutoff held for patients with congenital, neuromuscular and syndromic EOS. The cutoff for idiopathic EOS was 20 cm. For all patients, after the threshold was met, HRQoL continued to improve with increases in thoracic height at skeletal maturity. A subset of 169 patients for which arm span measurements were available was also identified and their thoracic heights were normalized. When grouped by the percentage of expected thoracic height attained, EOSQ-24 domains increased after a threshold of 80%. CONCLUSIONS: Once 18 cm of actual thoracic height or 80% of expected thoracic height is achieved, HRQoL continues to improve as thoracic height increases in skeletally mature patients with non-idiopathic EOS. Patients with idiopathic EOS had a higher threshold, possibly due to their larger average size and higher care giver expectations for HRQoL. LEVEL OF EVIDENCE: Level III.