A homogeneous population of 42 women with idiopathic scoliosis (mean age, 20.8 years and mean major thoracic curve of 58.2 degrees) had a complete pulmonary function test (PFT) at rest before, and a minimum of 3 years after, spinal fusion (mean, 7.7 years) to evaluate the effect of scoliosis and its surgical correction on PFT at rest. A multifactorial analysis showed that only the vital capacity (VC) was significantly lowered to 81% of predicted value (P less than 0.05). All of the other parameters of pulmonary volumes, flow, and gas exchanges, where corrected for the loss of lung volume, were within normal limits, showing pure restrictive changes in this population. Double-major curves were more severe, but no significant difference in PFTs were found with single thoracic curves. Curves over 50 degrees had significantly lower VC. The surgical correction of 40% is permanent and the functional improvement in postoperative vital capacity (VC) of 12% is significant (P less than 0.05). Other factors, such as the time between the two evaluations, the age of the patient, pelvic obliquity, trunk imbalance, and degree of kyphosis did not have any correlation with the observed changed on any of the PFT results. Therefore, early correction by spinal fusion in idiopathic scoliosis brings on some improvement of the vital capacity at rest and may prevent deterioration with progression of the curve.