This study analyzed the accuracy of Risser sign staging on posteroanterior radiographs. To correlate the Risser sign on a posteroanterior radiograph with that on an anteroposterior radiograph. On the posteroanterior view of the spine, the full length of iliac apophysis is difficult to interpret. No report has assessed the relation of these findings. The staging of the Risser sign was examined in 89 girls. In 52 subjects, the stage of the Risser sign was identical on both views, whereas in 37 (42%) the interpretations were different. On evaluation of the iliac apophysis using a skeletal specimen, the posteroanterior views produced a distorted image of the iliac apophysis, and the medial and lateral aspects of the apophysis were superimposed over the ilium. As a result of these findings and the fact that the Risser staging was developed for the anteroposterior radiograph, the appearance of the iliac apophysis on the posteroanterior radiograph cannot be used as a reliable indicator of skeletal maturity.