The aim of the PHQ is to facilitate the recognition and diagnosis of the most common mental disorders in primary care. The users of the PHQ are therefore primarily medical practitioners. The background to this choice of target group is that doctors (in private practice) are often consulted first in the case of psychological problems, or that there is often a psychological comorbidity in the case of somatic illnesses. Studies show, however, that mental disorders are often not or not correctly recognized by physicians (cf. e.g., Thompson, Kinmonth, Stevens, Peveler, Stevens, Ostler, Pickering, Baker, Henson, Preece, Cooper & Campbell, 2000). In order to ensure adequate treatment of patients' mental health problems as well, the PHQ is intended to provide an instrument to help change this condition. The questionnaire enables the detection of somatoform disorders, depressive disorders, anxiety disorders, eating disorders and alcohol abuse/dependence. However, the data obtained in the questionnaire should be deepened and substantiated in the interview. The PHQ can be used to assign diagnoses according to ICD-10 or DSM-IV, for which a table is provided in the test manual (p. 9). The PHQ is suitable for status and course diagnostics both for practical use and for research questions. The American version has found wide use in various studies, as numerous publications show (cf. e.g. e.g. Goodwin & Olfson, 2002; Rollman, Hanusa, Lowe, Gilbert, Kapoor & Schulberg, 2002). The test can be performed individually or in groups. Patients complete the test on their own. About 10 to 15 minutes are needed for the long form and about five minutes for the short form. The "Patient Health Questionnaire (PHQ)" can be used in its complete or short form as a psychodiagnostic instrument in clinical practice and in the context of research questions. It is suitable for both initial diagnosis and follow-up assessment of mental disorders. If the PHQ is used as a screening instrument in clinical practice, it should be presented to all patients if possible. In this way, a screening of mental disorders is possible that is independent of previous findings and enables the diagnosis of mental disorders in previously unremarkable patients. It makes sense to exclude only those patients who are unable to complete the questionnaire due to their physical condition or who have already completed the questionnaire within the last year.