Abstract Background Severe scoliosis can affect respiratory function in growing patients and produce cardiopulmonary complications, leading to significant morbidity. The development of spinal deformity may impact on young patients’ level of function and reported quality of life (QOL). The aim of this study was to investigate the relationship between lung function, exercise capacity and quality of life in young patients with spinal deformity. Methods This is a retrospective analysis of 104 patients (31% male, 69% female with mean age 14.9yrs). 77% of patients had an adolescent idiopathic scoliosis, with the remainder having other scoliosis diagnoses or Scheuermann’s kyphosis. Principal outcomes included Spirometry [FEV1, FVC], Whole Body Plethysmography, Cardiopulmonary Exercise Testing [CPET] and patient outcome questionnaires (with SRS-22). CPET measures included maximal exercise capacity [VO2peak] as well as VO2 at ventilatory threshold [VT] expressed as %predicted VO2max-a measure of physical conditioning, and minute ventilation [VE] from which breathing reserve [BR] could be calculated. Results Mean (±SD) main thoracic scoliosis was 59.9⁰ (±15.2⁰), and mean kyphosis in those with Scheuermann’s condition was 95.3⁰ (±11.5⁰). No correlation was elicited between FEV1 or FVC (%predicted) and VO2peak (%predicted) in this patient cohort. Greater thoracic curves were associated with lower FEV1 (%predicted), r = −0.343, p = 0.001, FVC (%predicted), r = −0.307, p = 0.003 and BR (%) at the end of exercise (r = −0.-0.459, p < 0.001). The patient cohort had a mean (sd) VO2peak of 98(17) %predicted, with greater VO2peak levels recorded in female subjects, those of younger age and those with higher scoliosis angles. Those with better lung function [FEV1 (%predicted)] had better BR (%) at the end of exercise (r = 0.483, p < 0.001). SRS-22 scores correlated significantly with VO2peak (%predicted) (total SRS-22 versus VO2peak (%predicted), r = 0.336, p = 0.002). Conclusion Larger thoracic scoliotic curves are associated with poorer lung function but better exercise capacity, likely related to higher levels of physical conditioning. Higher QOL scores were recorded in patients who had greater VO2peak levels, suggesting that exercise capacity may be a protective factor for emotional well-being in patients with spinal deformity.