Tehran University of Medical Sciences Iranian Journal of Psychiatry 1735-4587 14 2 2019 05 08 171 178 EN Abolfazl Mohammadi Department of Psychiatry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Mehdi Soleimani Department of Psychiatry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran Mohammad Reza Mohammadi Department of Psychiatry, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Imaneh Abasi Department of Clinical Psychology, School of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Ali Akbar Foroughi Department of Clinical Psychology, Kermanshah University of Medical Sciences, Kermanshah, Iran. 2017 07 03 Objective: Cognitive-behavioral interventions have been used as effective approaches for the treatment and prevention of depression and anxiety. However, to date, no anxiety and depression prevention guidelines package has been developed for Iranian adolescents. Thus, the purpose of this study was to develop transdiagnostic prevention program of anxiety and depression for Iranian adolescents and to assess the effectiveness of this program in a sample of adolescents. Method: Based on evidence-based literatures on CBT interventions, transdiagnostic prevention program was developed and its content and face validity was assessed and established by 3 clinical psychologies (Ph.D.) and a psychiatrist (child and adolescent postdoctoral). Then, in a semi-experimental design, 62 students were recruited from a school in Tehran by purposive sampling method and were randomly assigned in to experimental (n = 40) and control (n = 22) groups. They participated in 8 sessions of intervention based on the developed program. Revised Child Anxiety and Depression Scale (RCADS)- Child Version and Parent Version- were used to gather the data before, after, and 3 months after intervention. Results: Results of ANCOVA, controlling for the effect of pretest score, showed no significant differences (P>0.05) between experimental and control groups in SAD, panic, MDD, separation anxiety, GAD, OCD, total anxiety, and total anxiety-depression for parent and child in pretest and posttest. Conclusion: Transdiagnostic prevention package for anxiety and depression had no significant effect on reducing anxiety and depression of adolescents. Using an inappropriate measure, difficulties with timing of assessment, and lower severity of pre-intervention anxiety and depression due to universal prevention and sample recruited, might have affected the present findings. Discussion would be clearer and more complete by analyzing follow-up results and education performance in the future. https://ijps.tums.ac.ir/index.php/ijps/article/view/1124 https://ijps.tums.ac.ir/index.php/ijps/article/download/1124/871