To evaluate the clinical usefulness of the Korean Developmental Screening Test (K-DST) via comparison with Korean Ages and Stages Questionnaire (K-ASQ) for the diagnosis of developmental delay in pediatric patients.The K-DST and K-ASQ were used to screen pediatric patients who visited the hospital for evaluation and diagnosis of delayed development. Korean Bayley Scales of Infant Development-II (K-BSID-II) or Korean Wechsler Preschool and Primary Scale of Intelligence III (K-WPPSI-III) were used for the standardized assessment. Moreover, the final clinical diagnosis was confirmed by three expert physicians (rehabilitation doctor, psychiatrist, and neurologist). The sensitivity and specificity of each screening tool for the final diagnosis were investigated and correlated with standardized assessments.A total of 145 pediatric consultations were conducted, which included 123 developmental disorders (40 autism spectrum disorders, 46 global developmental delay/intellectual disability, and 37 developmental language disorders) and another 22 that were not associated with any such disorders. The sensitivity and specificity of K-DST based on the final clinical diagnosis were 82.9% and 90.9%, respectively, which were not significantly different from that of K-ASQ (83.7% and 77.3%). Both K-DST and K-ASQ showed good correlation with K-BSID-II and K-WPPSI-III. No significant difference was found between the K-DST and K-ASQ measures.K-DST is an excellent screening tool and is expected to replace K-ASQ with high validity.