We retrospectively studied 43 adolescent boys treated with orthoses for idiopathic scoliosis to assess the usefulness of the timing of peak height velocity for predicting growth remaining and the likelihood of curve progression when compared with Risser sign, closure of the triradiate cartilage, and chronologic age. We compared the peak height velocity data in boys to our previous work for girls with adolescent idiopathic scoliosis. We found the median height velocity plots showed a similar high peak and sharp decline as is found in girls. All 13 patients with a curve magnitude > 30 degrees at the time of peak height velocity had progression of their scoliosis to > 45 degrees despite bracing. Four of 29 patients (14%) with curves < or = 30 degrees at peak height velocity progressed to 45 degrees. These values generate a sensitivity of 76%, specificity of 100% and accuracy of 91% in predicting progression to 45 degrees. Similar values have been found in female patients. The use of peak height velocity to predict the length of time for remaining growth was superior to Risser sign and chronologic age for boys with idiopathic scoliosis. Closure of the triradiate cartilage approximated the timing of peak height velocity in boys.