The use of measurement scales or questionnaires is common and is often seen as a panacea for assessing occupational risks in the psychosocial sphere. However, these tools should be reserved for very specific stages of a psychosocial risk prevention (PSR) process, and their selection from among the available scales must be based on specific criteria. Before initiating a prevention program, it will be possible to use certain existing data within the company during the essential pre-diagnostic stage. Analysis of this data will help determine whether to initiate a prevention program, which will first require an in-depth assessment. This assessment must evaluate, on the one hand, the stressors experienced at work (and, if possible, the sources of these stressors) and, on the other hand, the health status of employees (presence of chronic stress, anxiety-depressive disorders, etc.). The assessment of perceived stressors can be based on interviews or existing scales such as those developed by Karasek and Siegrist. To evaluate the level of chronic stress, validated questionnaires are also available that rate physiological and/or psychological symptoms; and if the situation has already deteriorated, the impact on health can be explored using mental health scales. (R.A.)