OBJECTIVE: To investigate the risk factors for Type II respiratory failure associated with severe scoliosis in patients under 40 years of age. METHODS: Patients with severe scoliosis and pulmonary impairment treated in our hospital from January 2020 to December 2022 were recorded. We evaluated the spinal parameters in standing full spine X-rays, including the main thoracic curve, thoracic kyphosis, apical vertebrae, and distance between T1-T12. We also assessed the patient's pulmonary function test (PFT), including forced vital capacity (FVC) and the percentage of measured FVC values to predicted values (FVC%). RESULTS: The study included 64 patients with severe and rigid scoliosis accompanied by severe pulmonary impairment. They were divided into two groups: Group 1 comprised 22 patients with Type II respiratory failure, and Group 2 comprised the remaining 42 patients without respiratory failure. The average age of onset for the two groups was 2.3 ± 2.9 years and 4.0 ± 4.5 years, respectively. The range of the apical vertebrae in Group 1 was from T6 to T11, and the range in Group 2 was the same. There was no significant difference in the main curve and kyphosis angle between the two groups. The average T1-T12 distances for the two groups were 130.3 ± 32.7 mm and 148.2 ± 37.6 mm, respectively. The PFT results indicated that all patients had severe pulmonary function impairment. Multivariate logistic regression analysis revealed that a T1-T12 distance of less than 100 mm was an independent risk factor for Type II respiratory failure. CONCLUSIONS: If not treated properly, early onset scoliosis would have a severe impact on pulmonary function. The T1-T12 distance was a risk factor for Type II respiratory failure associated with severe scoliosis in patients under 40 years old.