Background: Psychotic experiences (PEs) are common in help-seeking youths with non-psychotic mental health problems, yet the clinical importance of PEs as potential effect modifiers of psychotherapy interventions has been scarcely examined. We examined if PEs were associated with a differential response to transdiagnostic cognitive behavioural therapy (CBT) aimed at common emotional and behavioural problems. Methods: We present secondary analyses from the Mind My Mind (MMM) trial that randomized 396, 6-16-year-old youths to either 9–13 sessions of transdiagnostic modular community-based CBT (MMM) or community-based management as usual (MAU). MMM was superior to MAU in reducing parent-reported impact of mental health problems according to the Strengths and Difficulties Questionnaire (SDQ). PEs were assessed by semi-structured screening interviews at baseline. The contrast between subgroups (presence/absence of PEs) was calculated to test if PEs are potential effect modifiers regarding the change in parent-reported SDQ-impact (primary outcome, rated 0[low]-10[high]) and other SDQ-related outcomes. Results: Baseline PEs were present in 74 (19%) of youths. The superior effect of MMM on changes in SDQ-impact from baseline to week 18 was not effect modified by the presence of PEs (PEs[yes] −0.89 [95%CI −1.77;-0.01] vs. PEs[no] −1.10 [95%CI −1.52;-0.68], p-value for interaction.68). For secondary outcomes similar patterns were observed. Limitations Statistical power was limited to show if PEs modified treatment response. Replication and meta-analytic evidence are needed. Conclusions: The beneficial effects of MMM transdiagnostic CBT did not differ by PE-status, indicating that youths with emotional and behavioural problems could be offered such psychotherapy irrespective of co-occurring PEs.