Background Little is known about the impact of being a bystander to bullying. This study compared health outcomes among bullies, victims and bystanders, and investigated actions taken by bystanders when they saw bullying. Method Participants included 7522 students aged 12-18 years that completed self-report questionnaires in the 2013/ 2014 Health Behaviour in School-aged Children survey. Binary logistic regression models (controlled for bully, victim, bystander status and demographic variables) were used to investigate the associations between participation in bullying as a bully, victim and bystander and health outcomes. Results Overall, 13.3% of adolescents reported being a bully, 25.1% reported being a victim and 30.5% reported that they saw bullying, in the last couple of months. Bystanders were significantly more likely to experience psychological symptoms (OR 1.355), somatic symptoms (OR 1.392) and low life satisfaction (OR 1.268) than those who were not bystanders. Helping the victim was significantly associated with experiencing psychological symptoms (OR 1.240), somatic symptoms (OR 1.251) and low life satisfaction (OR 1.198). Being a bully was significantly associated with experiencing psychological symptoms (OR 1.382) and not having excellent health (OR 1.252). Victims were significantly more likely to experience psychological symptoms (OR 2.437), somatic symptoms (OR 2.364), low life satisfaction (OR 2.564) and not having excellent health (OR 1.559). Conclusion In Ireland, being a bystander to bullying is more prevalent in schools than bullying perpetration or victimisation. The impact of being a bystander to bullying needs to be highlighted and included in intervention development.