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Abstract: Aim and Background: The exact review of the prevalence of internalized and externalized disorders in adolescence is essential to design and prepares appropriate remedial services that aimed at reducing the negative consequences and subsequent growth of mental disorders and improving adolescent functioning. The aim of this study is investigation of prevalence of internalized and externalized behavioral problems among middle school boys Zanjan city. Methods and Materials: The study population consisted of all male students in Zanjan middle schools in the academic year 91-90 . For sampling, by using random cluster sampling 300 students were selected as sample and Achenbach Adolescent self-evaluation questionnaire (YSR) was completed by them. Finally, after excluding incomplete questionnaires, 292 completed questionnaires were entered into the analysis. Findings: Result showed that prevalence of internalized and externalized problems according to clinical classification , on a scale based on DSM are, respectively, 3 percent and 4.5 percent and According to the border classification, respectively, are 6.4 percent and 8 percent. In the clinical category of internalized disorders, the highest prevalence rate is somatization (8.2 percent) and in the clinical category of externalized disorders, the highest prevalence rate, is conduct disorder (8.2 percent). In the borderline category of internalized disorders, the highest prevalence rate is depression and in the externalized disorders, the highest prevalence rate, is oppositional defiant disorder. Conclusions: Considering that there are internalized and externalized problems among adolescents, the need for designing treatment and prevention programs is felt.