PURPOSE: As a preliminary study on the development of a new developmental screening tool, this study examined the validity of the Korean Ages and Stages Questionnaires (K-ASQ). METHODS: The clinical sample included a total of 218 Infants and children at 30, 36, 60 months of age, who were diagnosed with developmental disorders. Age- and sex-matched normal controls were selected from a national large-scale K-ASQ database. Sensitivity, specificity, and accuracy were calculated in different age and diagnosis groups, and receiver operating characteristic (ROC) curve analysis was performed as well. In addition, concurrent validity was analyzed for the clinical sample by comparing the K-ASQ with other reference scales. RESULTS: The sensitivity, specificity, and accuracy of the K-ASQ were above fair (0.82-0.96) overall, however they varied depending on age and diagnosis groups. Specifically, the sensitivity at 60 months was relatively low (0.65). Especially, the discrimination sensitivity for the language delay group was poor at 60 months (0.42). ROC analysis showed that the overall discrimination capacity was above fair in all 5 domains [area under the curve (AUC): 0.74-0.98]. However, there were some domains and age groups with relatively poor discrimination capacity. In terms of concurrent validity, the correlations between the K-ASQ domains and reference scale subscales were statistically significant overall, but weak in some domains. CONCLUSION: The overall discrimination capacity and concurrent validity of the K-ASQ were above fair, but there were some domains, age, and diagnosis groups in which the K-ASQ was not successful in identifying potentially developmentally challenged children. These findings suggested the need for the development of a new developmental screening test tool, which is suitable for Korean infants & children.