This study documents the need for wider use of treatment monitoring in the mental health field and presents clinicians with a valuable, brief tool for monitoring progress regarding depression, anxiety and anger, all on one page. Strong concurrent validation was established between the five-item Depression Scale of David Burns’ Brief Mood Survey (BMS) and the widely used but longer, 21-item Beck Depression Inventory–II (BDI-II). Strong validation was also found regarding the classification of depression severity (minimal, mild, moderate, and severe) between the two scales. Additionally, the sensitivity (using standard formulas) of the BMS Depression Scale in detecting “clinically significant” scores as defined by the BDI-II is 96% (i.e., the percentage of accurate detection by the BMS); its specificity is 83% (i.e., its freedom from incorrectly labeling a BDI-II “minimal depression” score as “clinically significant”), and its overall combined accuracy in differentiating “minimal” and “clinical classifications” is 92%. This research also shows that the BMS Anxiety Scale and BMS Anger Scale (both five items) correlate significantly with the respective subscales of Anxiety and Hostility on the Symptom Checklist–90–Revised (SCL-90-R), providing further valuable client information for clinicians. This means the BMS offers psychotherapists a much needed quick, efficient, valid, standardized instrument for identifying and assessing depression, and for monitoring treatment progress regarding depression, anxiety, and anger. Additionally, the five-item BMS Depression Scale by itself offers physicians and other health care professionals a valid, quick screening tool for detecting depression and assessing its severity.