The authors reviewed 43 patients with the onset of idiopathic scoliosis between 4 and 9 years who were followed to skeletal maturity to document the natural history, effects of bracing, and factors associated with progression. Average age at onset was 7.1 years for female and 6.7 for male patients. Twelve were treated with observation only; six improved, five progressed, and one refused an orthosis and required surgery. Thirty-one patients wore an orthosis; five patients improved or were unchanged, and 26 progressed, including 13 who subsequently required surgery. All patients treated with observation had a rib vertebral angle difference (RVAD) of less than 10 degrees; whereas patients progressing despite orthosis and all but one patient requiring operation had an RVAD greater than 10 degrees. Thoracic hypokyphosis (less than 20 degrees) was present in 20% of observed patients, 64% of those treated with an orthosis, and 78% of those requiring operation.