The link between depression and paranoia has long been discussed in the psychiatric literature. Because this association is difficult to study in patients with full-blown psychosis, we investigated clinical high-risk (CHR) patients.

To clarify the causal connection between depression and paranoia.

To investigate how clinical depression relates to presence and new occurrence of paranoid symptoms in CHR patients.

Altogether, 245 young help-seeking CHR patients were assessed for suspiciousness/paranoid symptoms with the Structured Interview for Prodromal Syndromes at baseline, 9-month and 18-month follow-up. At baseline, clinical diagnoses were assessed by the Structured Clinical Interview for DSM-IV, childhood stressful experiences by the Trauma and Distress Scale, trait of suspiciousness by the Schizotypal Personality Questionnaire, and anxiety and depressive symptoms by the Positive and Negative Syndrome Scale.

At baseline, 54.3 % of CHR patients reported at least moderate paranoid symptoms. At 9- and 18-month follow-ups, the corresponding figures were 28.3 % and 24.4 %. Depressive disorder, sexual abuse and anxiety symptoms associated with paranoid symptoms. Depressive, obsessive-compulsive and somatoform disorders, sexual abuse, and anxiety predicted occurrence of paranoid symptoms.

Depressive disorder is one of the major clinical factors associating with and predicting paranoid symptoms in CHR patients; also childhood sexual abuse and anxiety symptoms associate with paranoia. In addition, obsessive-compulsive and somatoform disorders seem to predict paranoid symptoms. Low self-esteem may be a common mediator between affective disorders and paranoia. Effective treatment of these disorders may alleviate paranoid symptoms and improve interpersonal functioning in CHR patients.