A retrospective analysis of adults treated with long instrumented fusion for scoliosis from the thoracic spine proximally to L4 or L5. To evaluate the long-term clinical outcomes as well as radiological changes in distal unfused mobile segments and to evaluate factors that may predispose to distal disc degeneration and/or poor outcome. A total of 151 mobile segments in 85 patients (65 female), mean age 43.2 (range 21-68), were studied. Curve type, number of fused levels and pelvic incidence were recorded. Clinical outcome was measured using the Whitecloud function scale and disc degeneration using the UCLA disc degeneration score. Spinal balance, local segmental angulations and lumbar lordosis were measured pre- and post-operatively as well as at the most recent follow up--mean 9.3 years (range 7-19). A total of 62% of patients had a good or excellent outcome. Eleven had a poor outcome of which ten underwent extension of fusion--five for pain alone, three for pain with stenosis and two for pseudarthroses. Pre-operative disc degeneration was often asymmetric and was slightly greater in older patients. Overall, there was a significant deterioration in disc degeneration (P < 0.0001) that did not correlate with clinical outcome. Disc degeneration correlated with the recent sagittal balance (Anova F = 14.285, P < 0.001) and the most recent lordosis (Anova F = 4.057, P = 0.048). The post-operative sagittal balance and local L5-S1 sagittal angulation correlated to L4 and L5 degeneration, respectively. There was no correlation between degeneration and age, pre-operative degenerative score, pelvic incidence, sacral slope, number of fused levels or distal level of fusion. Disc degeneration does occur below an arthrodesis for scoliosis in adults which does not correlate with clinical outcome. The correlation of loss of sagittal balance with disc degeneration may be as a result of degeneration causing the loss of balance or vice versa, i.e. sagittal imbalance causing degeneration. Immediate post-operative imbalance correlates with degeneration of the L4/5 disc, which may imply the latter.