Purpose This study investigated the prevalence of Internet addiction (IA) and cyberbullying and examined profiles of adolescents with increased risk to develop pathological behaviors. Methods In this cross-sectional, school-based study, 8053 students of 30 middle and 21 high schools (12–18 years old) were invited to participate, based on a multistage stratified random sampling technique. The Internet aiddiction test (IAT) was used along with information on socio-demographics, Internet activities and cyberbullying experience. Results Five thousand five hundred and ninety students participated (response rate 69.4%). Pathological Internet use (IAT ≥50) was found in 526 (10.1%), while 403 (7.3%) experienced cyberbullying as victims and 367 (6.6%) as perpetrators during the last year. In multivariable models, the odds of IA increased with online hours on mobile phones and Internet use during weekends, Internet café visits, chatrooms usage and engagement in cyberbullying. Cyberbullying victims were more likely to be older, female, Facebook and chatrooms users, while perpetrators were more likely to be male, older Internet users and fans of pornographic sites. A perpetrator was significantly more likely to have also been a victim [odds ratio (OR) = 5.51, confidence interval (CI): 3.92–7.74]. Hours of daily Internet use on a mobile phone was independently associated with IA and cyberbullying (OR) 1.41, 95% CI 1.30, 1.53 and OR 1.11, 95% CI 1.01, 1.21, respectively. Conclusions Cyberbullying is associated with IA and the hours spent online on a mobile phone affected both conditions. The increasing Internet access through mobile phones or other devices should be accompanied by the appropriate education of both parents and adolescents on safe Internet use.