The DetectaWeb-Distress Scale is a web-based scale for screening and detecting internalizing disorder symptoms (anxiety, depression, posttraumatic stress, obsessions and compulsions, and suicidality) in children and adolescents. Previous studies examined the validity and reliability of the scale, however, there are no data on its diagnostic validity. The objective of this study was to examine the evidence of diagnostic validity of the DetectaWeb-Distress scale in a sample of 244 children and adolescents from clinical (n = 51) and community (n = 193) settings, all of them with the diagnostic process completed. The results indicated that the DetectaWeb-Distress scale is a useful measure from a diagnostic point of view, as it discriminates between people with emotional disorders such as anxiety and depressive disorders and suicidality, and those without, presenting ROC values of approximately .80 and good sensitivity and specificity for detecting the main emotional disorders. The DetectaWeb-Distress Scale is a valid measure and diagnostically useful for detecting and identifying children and adolescents with anxiety disorders, depression and suicidality, with the advantage that it is a short measure, specifically developed for Internet use, especially relevant in the era of COVID-19.