UNLABELLED: Trauma and post-traumatic stress are involved in the aetiology and maintenance of voice-hearing. It has been proposed that trauma-focused therapy (TFT) might affect voice-hearing, but previous studies are limited and remain undecided. OBJECTIVES: We aimed to investigate the effect of TFT on voice-hearing in people with PTSD and psychosis using experience sampling method (ESM). A secondary aim was to explore how changes in voice-hearing are related to changes in PTSD. DESIGN: This is an adjunct longitudinal ESM study of a sub-group of participants (N = 39) from a randomised controlled trial that compared TFT to a waiting-list control group. METHODS: Voice-hearing participants filled in 10 daily voice-hearing-related questionnaires for six consecutive days at baseline and post-treatment at pseudo-random times during the day. PTSD symptom severity was assessed at baseline and post-treatment. Multilevel linear regression was used to test the effect of TFT on voice-hearing and to analyse the relationship between changes in voice-hearing and changes in PTSD. RESULTS: The intention-to-treat analysis showed a significant interaction effect between time and treatment condition (p <
.00001) with a small effect size (dppc2 = -0.27), indicating a larger decrease in voice-hearing in the TFT group than in the waiting-list control group. Also, a significant association was observed between changes in PTSD symptoms and changes in voice-hearing (p <
.00001). CONCLUSIONS: Our findings tentatively suggest that, even when voices are not targeted directly, TFT for PTSD can alleviate distressing voices.