Delusional beliefs in first admitters with no organic disorder are studied. The study sample of 88 patients provides a representation of delusional beliefs in first admitters. A scale for dimensions of delusional beliefs is proposed and applied to the patient group. The scale includes dimensions of conviction, extension, systematization, probability, pressure and global state. Adequate interobserver agreement is achieved. The patients are distributed according to ICD-10 and DSM-III-R with schizophrenia as the most frequent diagnostic category. More than half of the patients are, however, diagnosed differently. It is obvious that many patients with schizophrenia and persistent delusional disorder are seriously dysfunctioning at their entry into hospital. In contrast patients with affective disorder and acute and transient psychotic disorder are, on the average, functioning reasonably well. Identical delusional themes appear in different diagnostic categories while the dimensional severity of delusional beliefs varies from one category to another. When assessed at admission patients with a discharge diagnosis of schizophrenia have delusional beliefs with a high degree of dimensional severity in contrast to patients with affective disorder. Delusional beliefs in patients with persistent delusional disorder seem more systematized and probable than those diagnosed differently. In interpreting the findings one has to remember that the presence and theme of delusional beliefs are in no way independent aspects of diagnostic category. Description of delusional dimensions may, however, be important for the conceptualization of delusional beliefs and a method to study psychotic decompensation and resolution. Later on the patients were followed in search of the predictive significance of a qualified assessment of delusional beliefs in contrast to syndromes when defined according to new classification systems.