Large curves between 50 and 80 degrees progress after skeletal maturity in untrated idiopathic scoliosis. In patients treated surgically for idiopathic scoliosis, curves sometime progress after removal of spinal instrumentation. Twenty-seven patients were evaluated to quantitate curve progression after removal of spinal instrumentation and identify factors leading to curve progression. Curve progressed in nine out of the twenty-seven patients. Curve progression is related to only curve magnitude, and not to correction rate, interval between operation and removal of spinal instrumentation, age, Rissers sign, type of scoliosis (adolescent, juvenile, infantile) , and spinal balance.