Bullying negatively impacts the mental and physical health of student victims, bullies and bystanders. The Olweus Bullying Prevention Programme is an internationally recognized school based programme demonstrated effective in research. The purpose of this study was to determine if the Bullying Prevention Programme was effective for urban youth from diverse ethnic backgrounds. The programme was implemented in one large urban school district in the United States. Bullying incident density was used to evaluate programme outcomes. An independent evaluator performed 319 observation sets, 7,589 minutes. Data were standardized to incident density and reported back to school committees who developed and implemented culturally and developmentally relevant interventions based on the Olweus model. At baseline, incident density was 65 incidents per 100 student hours. After four years, incident density decreased by 45 percent to 36 incidents per 100 student hours. Programme components associated with decreased incidents were posting of rules, consistent enforcement of positive and negative consequences and training adult monitors to engage students in activities. Supplementary strategies were socialized recess, providing pro-social activities, reorganization of lunches and recess and separation of grades or genders. Results suggest that the Bullying Prevention Programme reduces incident density by up to 65 percent. (Contains 1 table.) [This research was supported by the Safe and Drug Free School and Community Act (Title 4).]