Background: Prader-Willi syndrome (PWS) is a genetic disorder with multisystemic involvement. Age-dependent subtle facial characteristics are noted, making it is difficult for physicians to recognize the syndrome. Computer-aided facial dysmorphism analysis, the Facial Dysmorphology Novel Analysis (FDNA), is an automated facial detection program associated with possible syndromes using 2D-photo. The FDNA was developed using pictorial data mainly from Caucasian individuals. This study intended to determine diagnostic yields of FDNA for Thai PWS patients and to compare the results before and after program training (PT). Methods: Patients with molecularly confirmed PWS were enrolled. Frontal facial photos were obtained and randomly divided into 2 groups: (I) training group and (II) test group.