[Between faith and delusion].

Religious beliefs can lead to difficulties in psychiatric diagnosis, when it comes to distinguishing between faith and delusion. Delusion is defined as a false assessment of reality combined with subjective certainty, which is in contrast with the reality of the social environment. The problem with this definition is that reality cannot be examined with scientific methods/criteria and that the assessment of reality itself underlies historical and cultural fluctuations. The current diagnostic manuals for psychiatric disorders DSM 5 and ICD-10 require, that the content of the belief has to be inadequate even in the subculture of the patient (ICD-10) and that the cultural and socioeconomic background of the patient has to be taken into account (DSM 5). On the basis of this case-report and of selected publications on this topic we want to discuss this diagnostic problem. After that we present a diagnostic model for delusion, which is easy to handle in the daily routine of psychiatrists.