We evaluated construct validity, responsiveness, and utility of change indicators of the Dutch-Flemish PROMIS adult v1.0 item banks for Depression and Anxiety administered as computerized adaptive test (CAT). Specifically, the CATs were compared to the Brief Symptom Inventory (BSI) using pre- and re-test data of adult patients treated for common mental disorders (N = 400; median pre-to-re-test interval = 215 days). Construct validity was evaluated with Pearson’s correlations and Cohen’s ds; responsiveness with Pearson’s correlations and pre-post effect sizes (ES); utility of change indicators with kappa coefficients and percentages of (dis)agreement. The results showed that the PROMIS CATs measure similar constructs as matching BSI scales. Under the assumption of measuring similar constructs, the CAT and BSI Depression scales were similarly responsive. For the Anxiety scales, we found a higher responsiveness for CAT (ES = 0.64) compared to the BSI (ES = 0.50). Finally, both CATs categorized the change scores of more patients as changed compared to matching BSI scales, indicating that the PROMIS CATs may be more able to detect actual change than the BSI. Based on these findings, the PROMIS CATs may be considered a modest improvement over matching BSI scales as tools for reviewing treatment progress with patients. We discuss several additional differences between the PROMIS CATs and the BSI to help test users choose instruments. These differences include the adopted measurement theory (Item Response Theory vs. Classical Test Theory), the mode of administration (CAT vs. fixed items), and the area of application (universal vs. predominantly clinical).