Thirty-one patients with idiopathic scoliosis were studied to identify changes in the nucleus pulposus(NP) using magnetic resonance imaging (MRI). The mean curvature and the mean age at initial assessment were 26and 12.6 years respectively. The mean follow-up time period after MRI scan was 3.6 years. Deviation of the NP near the apex of the curves was examined from two sets of MRI scans obtained before and after correction of the deformities. The subjects who showed good mobility or slight deviation of the NP(n=14) successfully completed brace treatment. Those subjects who showed an immobile NP(n=5) were shown to have progressive curves despite brace treatment. Unbraced subjects who showed mobility or slight deviation of the NP(n=10) demonstrated no progression at final follow-up. Two patients with Risser sign 4 and 2 years after menarche who showed an immobile NP were shown to have nonprogressive curves. The results indicate that deviation and mobility of the NP prior to application of a brace or prior to cessation of growth seem to be good prognostic indicators for curve progression.