Background: Growing-rod (GR) treatment is the current standard for progressive idiopathic early-onset scoliosis (I-EOS) in young children. Despite good radiographic outcomes, the impact of scoliosis treatment on pulmonary functions is not well-defined in this patient population. The aim of this study was to evaluate pulmonary functions and exercise tolerance in I-EOS patients graduated from GR treatment and to compare them with age-matched, surgically treated adolescent idiopathic scoliosis (AIS) patients and healthy controls. Methods: Eight GR graduates with I-EOS with pulmonary function tests and complete radiographic results were compared with a group of 9 thoracic AIS patients at least 2 years out from posterior fusion. Both groups were also compared with a set of 10 healthy individuals. All subjects underwent cardiopulmonary exercise testing and spirometry to evaluate pulmonary function. Results: Age, sex, height, arm span, weight, residual deformity, and level of instrumentation in GR and AIS patients were similar. In the GR group, forced vital capacity % and forced expiratory volume in 1 second % values were reduced compared with the healthy controls and AIS group (P<0.001, <0.001 and 0.036, 0.046, respectively). Breathing reserve index at lactate threshold (BRILT) was higher in GR and AIS patients (P=0.001 and 0.002, respectively), and was similar between GR and AIS patients (P=0.916). Heart rate at lactate threshold was higher in GR and AIS groups compared with controls (P<0.001 and 0.001, respectively). Conclusions: AIS and GR patients demonstrated reduced pulmonary reserve and exercise tolerance compared with their peers with no spinal deformity. However, exercise tolerance of I-EOS patients treated with the GR method was similar to that of operated AIS patients. These results suggest a positive impact of GR treatment in children with I-EOS.