International Journal of Preventive Medicine (Int J Prev Med)2008-7802002015022414841484EN20150224<strong>Background:</strong> This study aims to explore the frequency of aggressive behaviors among a nationally representative sample of Iranian children and adolescents.<br /><strong>Methods: </strong>This nationwide study was performed on a multi‑stage sample of 6&ndash;18 years students, living in 30 provinces in Iran. Students were asked to confdentially report the frequency of aggressive behaviors including physical fghting, bullying and being bullied in the previous&nbsp;<br />12 months, using the questionnaire of the World Health Organization Global School Health Survey.<br /><strong>Results:</strong> In this cross‑sectional study, 13,486 students completed the study (90.6% participation rate); they consisted of 49.2% girls and 75.6% urban residents. The mean age of participants was 12.47 years (95% confdence interval: 12.29, 12.65). In total, physical fght was more prevalent among boys than girls (48% vs. 31%, P &lt; 0.001). Higher rates of involvement in two other behaviors namely being bullied and bulling to other classmates had a higher frequency among boys compared to girls (29% vs. 25%, P &lt; 0.001 for being bullied) and (20%&nbsp;<br />vs. 14%, P &lt; 0.001 for bulling to others). Physical fghting was more prevalent among rural residents (40% vs. 39%, respectively, P = 0.61), while being bullied was more common among urban students (27% vs. 26%, respectively, P = 0.69).<br /><strong>Conclusions:</strong> Although in this study the frequency of aggressive behaviors was lower than many other populations, still these fndings emphasize on the importance of designing preventive interventions that target the students, especially in early adolescence, and to increase their awareness toward aggressive behaviors. Implications for future research and aggression prevention programming are recommended.<br /><strong>Keywords:</strong> Bullying, children and adolescents, Iran, physical fght, prevalence, violencehttp://ijpm.mui.ac.ir/index.php/ijpm/article/view/1484http://ijpm.mui.ac.ir/index.php/ijpm/article/download/1484/1766