Despite widespread evidence-based treatments for addressing internalizing concerns, many youth do not demonstrate reliable or clinically meaningful improvement. Regular progress monitoring, consisting of measurement and feedback, offers the opportunity to improve outcomes in real time. The 21-item Depression Anxiety and Stress Scales (DASS-21; Lovibond & Lovibond, 1995) has potential as a progress-monitoring tool for internalizing concerns in youth; however, limited psychometric data are available to support this use. The purpose of this study was to investigate the dependability of data obtained from the DASS-21 when completed by adolescents in a clinical setting. This study also aimed to understand the feasibility and utility of using the DASS-21 as a progress-monitoring tool from youth and clinicians' perspectives. Generalizability and dependability analyses were conducted to determine the number of ratings needed to obtain a dependable estimate of youth functioning within 1 week. Whereas two daily ratings were needed to dependably estimate total distress, results for the depression, anxiety, and stress subscales indicated that two to five data points would be needed over the course of the week. Finally, results demonstrate the usability of the DASS-21 from both youth and clinician perspectives when used in a progress-monitoring context.