Tehran University of Medical Sciences Iranian Journal of Psychiatry 1735-4587 21 2 2026 03 10 202 211 Farzin Malakooti Department of Psychology, University of Birjand, Birjand, Iran. Ahmad Khamesan Department of psychology, University of Birjand, Birjand, Iran Hadi Samadieh Department of Psychology, University of Birjand, Birjand, Iran. Mohammad Hossein Sorbi Department of Psychology, University of Birjand, Birjand, Iran. 2025 08 01 2025 10 18 Objective: Given the importance of mental health during adolescence and the considerable prevalence of psychological problems among this age group, along with the limited epidemiological data available in South Khorasan province, Iran, the present research focused on determining the prevalence of internalizing and externalizing problems in regional school-aged adolescents and analyzing related demographic characteristics. Method: This descriptive cross-sectional study included 1,152 adolescents aged 12 to 19 years (mean age = 15.42, SD = 1.65) from Birjand City. A multistage random sampling method was employed to select the participants. Data were collected using the self-report version of the Strengths and Difficulties Questionnaire (SDQ), which measures internalizing and externalizing problems. To analyze the data, descriptive statistics were computed and comparative analyses were performed. Demographic variables such as age, gender, academic performance, school grade, and school type were also included in the analysis. Results: The prevalence of internalizing problems among the participants was 36.8% (95% confidence interval: 34.0 to 39.6), whereas externalizing problems were identified in 15.2% (95% CI: 13.0 to 17.4). Internalizing problems were significantly more prevalent among girls (40.1%) than boys (32%). However, no significant gender difference was found in externalizing problems (girls: 14.5%, boys: 15.8%). Emotional problems (28.6%) and hyperactivity (10.4%) were significantly more common in girls, while peer problems (61.7%) and conduct problems (17.5%) were higher in boys (P < 0.01). Adolescents with poor academic performance and those attending public schools reported higher levels of psychological problems (P < 0.01). Conclusion: Internalizing problems are more common than externalizing problems among adolescents. The main risk factors include being female, poor academic performance, and attending public schools. Mental health programs and interventions should prioritize these high-risk subgroups to enhance preventive and therapeutic outcomes. https://ijps.tums.ac.ir/index.php/ijps/article/view/4339 https://ijps.tums.ac.ir/index.php/ijps/article/download/4339/1328