INTRODUCTION: Worry is common and distressing in psychotic disorders, contributing to the onset and persistence of persecutory delusions. A previously developed 8-week manualized cognitive behavioral therapy (CBT)-worry intervention has shown efficacy in treating persecutory delusions, compared with standard care. We aimed to test CBT-worry's impact on persecutory delusions at 8 weeks, as previously reported, delusions at 24 weeks, and secondary clinical outcomes, relative to an active comparison therapy. MATERIALS AND METHODS: A two-arm, assessor-blinded, randomized controlled trial was conducted. Sixty-two adults with a non-affective psychotic disorder and current persecutory delusion were randomized to CBT-worry (n = 32) or befriending (n = 30). The preregistered primary clinical outcome was persecutory delusion severity. Outcomes were assessed at baseline, post-treatment (8 weeks), and at follow-up (24 weeks). RESULTS: Regarding primary outcomes, CBT-worry was not superior to befriending in treating persecutory delusions at post-treatment or follow-up (P's > .05). For secondary exploratory outcomes, CBT-worry demonstrated superiority over befriending for self-reported worry (d = .26, P = .006), depression (d = .23, P = .018), perseveration (d = .21, P = .024), insomnia (d = .25, P = .01), and asocial beliefs (d = .23, P = .022) and assessor-rated affective symptoms (d = .36, P < .001) post-treatment. At follow-up, no significant between-group treatment effects were found after correction for multiple comparisons. DISCUSSION: A brief CBT-worry intervention did not outperform befriending in the treatment of persecutory delusions. CBT-worry did, however, demonstrate significant benefit for affective symptoms post-treatment, compared to befriending. At follow-up, gains were maintained in CBT-worry but were also observed in befriending, minimizing group differences. Limitations include a small sample size, lack of a non-clinical control, and 20% drop-out. ClinicalTrials.gov (NCT04748679).