Background: The purpose of this study was to provide data about the prevalence of violent behaviour among high school students living in Istanbul and to determine the correlates of physical fighting. Method: This study involved the completion of a modified version of 'Health Behaviour in School Age Children (HBSC) 1997/1998' survey questionnaire by 4153 grade 9-11 students. Chi square tests and forward stepwise multiple logistic regression models were used for statistical analyses. Results: During the last 12 months preceding the survey 42% of students (n=1720) reported that they had been in a physical fight; 7% (n=274) reported that they were involved in a fight which required medical treatment. During the last school term 19% (n=768) bullied others at school; 30% (n=1255) reported having been bullied at school; 7% (n=309) reported that they had been bullied with a weapon on school grounds; 8% (n=346) reported that they carried a weapon on school grounds. In logistic regression analyses being male, poor mental health score, being sexually active, current cigarette use, illicit drug use, not using seat belts, bullying, being bullied with a weapon, carrying a weapon, spending more time with friends, poor school image and physical abuse were found to be associated with fighting. Conclusion: Violent behaviour is common in high school students. There is a strong need for violence prevention programmes in schools.