Reactive psychosis is a common diagnosis in the Nordic countries (Norway, Sweden, Denmark, Finland and Iceland) and in several other parts of the world. In ICD-9 and DSM-III-R, the concept is defined more narrowly than in the Nordic tradition. In this study we examined the interrater reliability of the Nordic concept by the case-summary method between clinicians from 9 university departments in the Nordic countries. The results show that Nordic psychiatrists have a reasonably reliable concept of reactive psychosis, and that this psychosis can be diagnosed as reliably as schizophrenia and affective psychosis.