We aimed to determine the curve progression risk of idiopathic scoliosis in patients at the time of peak height velocity by plotting curve magnitudes against olecranon stages of skeletal maturation. Register data of 372 patients with juvenile or adolescent idiopathic scoliosis followed at 6-month intervals from onset of scoliosis to skeletal maturity were reviewed. At the onset of the pubertal growth spurt, curves greater than 30° have a 100% risk of progressing over 45° (P<0.0001). Curves 21–30° have a progression risk of 72.5% (P=0.0034). A curve progression velocity 6–10° per year represents a risk of 71.8% (P=0.0001) to require surgical treatment and a velocity greater than 10° per year represents a risk of 100% (P<0.0001). Plotting curve magnitudes against height measurements and the stages of olecranon maturation offers a reliable prediction of curve progression risk in idiopathic scoliosis during Risser 0.