<jats:sec id="S205647241900067X_sec_a1"> <jats:title>Background</jats:title> <jats:p>The period before the formation of a persecutory delusion may provide causal insights. Patient accounts are invaluable in informing this understanding.</jats:p> </jats:sec> <jats:sec id="S205647241900067X_sec_a2"> <jats:title>Aims</jats:title> <jats:p>To inform the understanding of delusion formation, we asked patients about the occurrence of potential causal factors – identified from a cognitive model – before delusion onset.</jats:p> </jats:sec> <jats:sec id="S205647241900067X_sec_a3" sec-type="methods"> <jats:title>Method</jats:title> <jats:p>A total of 100 patients with persecutory delusions completed a checklist about their subjective experiences in the weeks before belief onset. The checklist included items concerning worry, images, low self-esteem, poor sleep, mood dysregulation, dissociation, manic-type symptoms, aberrant salience, hallucinations, substance use and stressors. Time to reach certainty in the delusion was also assessed.</jats:p> </jats:sec> <jats:sec id="S205647241900067X_sec_a4" sec-type="results"> <jats:title>Results</jats:title> <jats:p>Most commonly it took patients several months to reach delusion certainty (<jats:italic>n</jats:italic> = 30), although other patients took a few weeks (<jats:italic>n</jats:italic> = 24), years (<jats:italic>n</jats:italic> = 21), knew instantly (<jats:italic>n</jats:italic> = 17) or took a few days (<jats:italic>n</jats:italic> = 6). The most frequent experiences occurring before delusion onset were: low self-confidence (<jats:italic>n</jats:italic> = 84); excessive worry (<jats:italic>n</jats:italic> = 80); not feeling like normal self (<jats:italic>n</jats:italic> = 77); difficulties concentrating (<jats:italic>n</jats:italic> = 77); going over problems again and again (<jats:italic>n</jats:italic> = 75); being very negative about the self (<jats:italic>n</jats:italic> = 75); images of bad things happening (<jats:italic>n</jats:italic> = 75); and sleep problems (<jats:italic>n</jats:italic> = 75). The average number of experiences occurring was high (mean 23.5, s.d. = 8.7). The experiences clustered into six main types, with patients reporting an average of 5.4 (s.d. = 1.0) different types.</jats:p> </jats:sec> <jats:sec id="S205647241900067X_sec_a5" sec-type="conclusion"> <jats:title>Conclusions</jats:title> <jats:p>Patients report numerous different experiences in the period before full persecutory delusion onset that could be contributory causal factors, consistent with a complex multifactorial view of delusion occurrence. This study, however, relied on retrospective self-report and could not determine causality.</jats:p> </jats:sec> <jats:sec id="S205647241900067X_sec_a6"> <jats:title>Declaration of interest</jats:title> <jats:p>None.</jats:p> </jats:sec>