Northern Ireland, unlike the Republic of Ireland or England, has no province-wide information on bullying in schools. This study provided baseline information on this complex issue across 120 schools in all five Education and Library Boards in Northern Ireland, comprising 60 primary and 60 post-primary schools, 1079 primary pupils (Year 6) and 1353 post-primary pupils (Year 9). In primary schools 40% of pupils and 30% of post-primary pupils reported being bullied at school; and 25% of primary and 28% of post-primary pupils admitted to bullying others. The results have brought the nature and extent of the issue to light and provide an evidential basis from which a coordinated strategy to tackle bullying can be developed.