We reviewed the medical records and roentgenograms of 1020 patients who had been managed for adolescent idiopathic scoliosis, between January 1954 and December 1979, with a Milwaukee brace; we wished to determine whether use of the brace had effectively altered the natural history of the disease. The findings were considered with respect to a previous study of 727 children who had had comparable curves and had not initially been managed with the brace but had been followed for progression of the curve, during the same time- span as that in the current study. Of those 727 patients, 558 (77 per cent) had no progression of the curve. The average age of the 1020 patients at the time that treatment with the brace was begun was thirteen and one-half years (range, ten to seventeen years). None of the patients had received any other treatment, and all had been managed only by the physicians participating in this study. In both the current and the earlier series, the outcome was considered a failure if the curve had increased 5 degrees or more; in the patients in the current study, who were managed with the brace, the outcome was also considered a failure if operative intervention had been needed. Of the 1020 patients in the current series, 229 (22 per cent) had operative intervention; this rate was higher in the patients who had a curve of more than 30 degrees at the time of bracing and in those who had a Risser sign of 0 or 1. The 791 remaining patients, who were managed with the brace only, had a mild improvement of 1 to 4 degrees at the time that use of the brace was discontinued (the difference being within the margin of error of measurement). With respect to curves of between 20 and 39 degrees, the rate of failure was lower in the current series of patients who had been managed with the brace than in the earlier series of patients who had not been thus managed but had been followed for progression. Progression of the curve was found to be related to the pattern and magnitude of the curve; the age of the patient at the time of presentation; the Risser sign; and, in girls, the menarchal status. We recommend that immature adolescents who have a curve of more than 25 degrees and a Risser sign of 0 be managed with a brace immediately, rather than after progression has been documented.