The exact evaluation of the mechanism of velopharyngeal valving in VPI patient is essential to the selection of treatment method and satisfactory result of the treatment. For this purpose several kinds of radiological techniques were developed such as lateral cephalogram, cinefluoroscopy and recently videofluoroscopy. But the poor quality of the image obtained by above methods has made the evaluation of the dynamic velopharyngeal sphinteric mechanism unsatisfactory. So authors tried to introduce new radiological technique of digital subtraction velopharyngography. With this technique, exact evaluation of velopharyngeal valving mechanism including LPWM(lateral pharyngeal wall movement) was possible, and we could choose the most appropriate treatment method.