Objective: There is a need for a simple and brief tool that can be used in routine clinical practice for the quantitative measurement of mental state across all diagnostic groups. The main utilities of such a tool would be to provide a global metric for the mental state examination, and to monitor the progression over time using this metric. Method: We developed the mental state examination scale (MSES), and used it in an acute inpatient setting in routine clinical work to test its initial feasibility. Results: Using a clinical case, the utility of MSES is demonstrated in this paper. When managing the patient described, the MSES assisted the clinician to assess the initial mental state, track the progress of the recovery, and make timely treatment decisions by quantifying the components of the mental state examination. Conclusion: MSES may enhance the quality of clinical practice for clinicians, and potentially serve as an index of universal mental healthcare outcome that can be used in clinical practice, service evaluation, and healthcare economics.