The Youth Australian and New Zealand Evaluation of Fitness to Stand Trial–Revised (Youth ANZ–EFST–R) was developed to address the lack of forensic assessment standardisation. Following development, 36 legal and mental health practitioners reviewed the proposed interview items to test the face, content and factor validity. Overall, 71% of items passed the validity thresholds. Items with poor validity related to the courtroom layout and psychotic symptoms affecting the defendant’s communication. Removing these items resulted in a 93% validity pass rate. There was moderate agreement about the proposed factor structure despite randomising the order and blinding participants to the administration rules (Gwet’s AC2 = .61, p < .001). The results provide preliminary support for the Youth ANZ–EFST–R with specified refinements made to enhance validity. Key limitations include the small sample size and the assumption of no crossloading items despite overlaps between the Presser criteria.