People with a severe mental illness often experience negative symptoms, such as reduced motivation / interest and blunted affect. Usually these symptoms are measured by observations. A drawback of this method can be found in the fact that observations are highly influential by experience and expertise of the observer. One way to overcome this limitation is by using a self-reporting questionnaire; the Self-Evaluation of Negative Symptoms (SNS). This questionnaire is originally written in French and has been translated in many languages. However, a Dutch version has not been created yet. In this project, we test the reliability and validity of the Dutch translation of the SNS. The article about the original questionnaire can be found here.