The editors first describe the principal symptoms of the Capgras delusion, the FrÉgoli delusion, the delusion of intermeta-morphosis and the delusion of subjective doubles before developing the argument that it would be appropriate for international psychiatric diagnostic systems to include these disorders. Furthermore the similarity between them, the reduplicative paramnesias and dÉjÀ and jamais vu are pointed out. By stressing a symptom-based approach it is possible to examine psychiatric, neurological and medical cases as arising from the same underlying disturbance in cognition function. The relationship between delusions of misidentification and other delusions is also touched upon.

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In the present paper the author will try to elucidate the stability of nosological categories as revealed by a personal follow-up investigation of 301 previously hospitalized patients with paranoid psychoses. Since the terminology used will be the Scandinavian one, a short review of the diagnostic concepts will be given. The Scandinavian concept of schizophrenia is rather narrower than that employed in the rest of Europe, and especially narrower than that prevailing in the Anglo-American literature. Many American authors include in their concept of schizophrenia what may be called “the schizophrenic reaction types”. In the present paper, the concept of schizophrenia used by Langfeldt (1937, 1939), sometimes, referred to as “process schizophrenia” or “nuclear schizophrenia” is used. “Primary symptoms” occur in clear consciousness; these include disturbances of thinking, disintegration of emotions, autism, marked feeling of influence and passivity, massive depersonalization and derealization. As a rule the illness has an insidious development and a chronic course ending up with a greater or lesser degree of mental deterioration.

A sample of 72 first-admitted patients with delusional disorder was personally re-examined after a mean of 10 years, and 42 of them after an average of 27 years. The mean observation period for all patients from admission to last follow-up was 20 years (3-39). There was a trend that patients with delusions of jealousy did better on course variables, but similar outcomes were revealed in groups with delusions of jealousy, persecution and a mixed group with different main delusions. Duration of symptoms prior to admission was a significant predictor of outcome, indicating dividing lines of 1 and 6 months at 10-year follow-up and 3 and 6 months at long-term follow-up. Based on the data, a minimal duration of 6 months is proposed for persistent delusional disorder.

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.