This study assessed the screening utility of the 12-item Short-Form Health Survey's (SF-12) mental health component scale (MCS-12) for diagnosable depression and anxiety disorders in a general population sample, and thus, the validity of this scale as a measure of mental health in epidemiological research. Data were from the Australian National Survey of Mental Health and Wellbeing (N=10,504). Diagnoses were made using the Composite International Diagnostic Interview. The MCS-12 was compared to other brief scales: the RAND Mental Health Component scale (RAND MHC-12, an alternative scoring method for the MCS-12), the 12-item General Health Questionnaire (GHQ-12), the Kessler Psychological Distress Scale (K10 and K6), and an estimate of the Mental Health Inventory (MHI-5). The MCS-12 and RAND MHC-12 were equally able to discriminate respondents with the target diagnoses. The MCS-12 performed better than the GHQ-12, and equally to the K6 for diagnoses of depression, though not anxiety disorders, where the K6 showed greater utility. The K10 out-performed the MCS-12 for all diagnoses. Areas under receiver operating characteristics curves (AUC) indicated that the MCS-12 is valid measure of mental health in epidemiological research, and a useful screening tool for both depression (AUC=0.92) and anxiety disorders (AUC=0.83).