The ventilatory functional restrictions during a maximal exercise tolerance test were investigated in 37 idiopathic scoliosis patients with curves <45° Cobb. Similar studies were performed in a control group of 10 healthy girls matched in age. There were no differences between scoliotic and healthy girls in basal ventilatory parameters (FVC, FEV1). However, adolescents with idiopathic scoliosis showed worse tolerance to exercise test with lower maximal speed average, lower ventilatory efficiency at maximal exercise, early anaerobic threshold, and a lower aerobic. Maximal died volume correlated to the severity of the scoliotic curve. When ventilatory efficiency was considered by the VE/VO2 ratio, scoliotic girls disclosed higher values than control, indicating an inefficiency in their ventilation. Patients wearing a brace at the time of ventilatory functional assessment did not exhibit any difference in the parameters investigated both at basal spirometry and during exercise tolerance test. Respiratory inefficiency together with lower ventilation capacity and lower VO2 max may be responsible for reduced exercise tolerance in adolescents with idiopathic scoliosis. Exercise deconditioning in scoliotic patients cannot be attributed to brace treatment.