Proximal junctional disease is a well-recognized postoperative phenomenon in adults who are undergoing long thoracolumbar fusion and instrumentation, and is attributed to increased a junctional stress concentration. In general, the onset of symptoms in these patients is insidious and the disease progresses slowly. We report on a contrary case of rapidly progressing paraplegia secondary to acute disc herniation at the proximal adjacent segment after long posterior thoracolumbar fusion with cement augmentation at the upper instrumented vertebra and the supra-adjacent vertebra. The patient was treated with a discectomy through the costo-transverse approach combined with extension of the posterior instrumentation. The patient's neurological status improved markedly. Stress concentration at the proximal junction disc space may have caused accelerated disc degeneration which in turn lead to this complication.