Several multi-dimensional self-report scales have been developed to assess delusional ideation in the general population. However, self-ratings of positive symptoms in patients with psychosis are often considered unreliable due to neuro-cognitive disturbance and lack of insight. This study tested associations of self- and observer-rated delusions as well as factors associated with discrepancies. Observer-rated delusions were assessed in 80 in- and outpatients with schizophrenia spectrum disorders by trained raters with the Positive and Negative Syndrome Scale. Self-rated delusions were assessed with the Peters et al. Delusions Inventory and the Paranoia Checklist. Correlations between self- and observer-rated overall delusions ranged from 0.49 to 0.57. Associations between specific delusions of persecution and grandiosity were moderate but unique. Good concordance of ratings was not restricted to outpatients or patients with fewer positive symptoms. Patients with lower self- than observer ratings of delusions were characterised by fewer years of education, lower functioning, more negative symptoms and less insight. The results indicate that patients can reliably provide information with regard to the presence and type of delusional beliefs. Thus, patient ratings are a valid additional source of diagnostic information.

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