Detection of depression is a major issue for public health. In a study performed in the HUG, we tested the concordance of the self-report Patient Health Questionnaire (PHQ-9) with the Hamilton depression scale (HDRS) administered by a psychiatrist, as measures of the severity of depression. The comparison shows that the PHQ-9 distinguishes subjects with and without depressive disorders and is a good screener for severe disorders but has a poor capacity of discrimination when disorders are mild. This instrument is insufficient if the aim is to detect mild or moderate depressive disorders, wich is the most frequent occurrence in patients consulting primary care physicians.