To examine the secondary effects of a personality-targeted intervention on bullying and harms among adolescent victims and bullies. Outcomes were examined for victims and bullies in the Climate and Preventure study, Australia. Participants completed self-report measures at baseline and four follow-up assessments (6, 12, 24, and 36 months). Thirteen intervention schools (n= 1,087) received Preventure, a brief personality-targeted cognitive-behavioral therapy intervention for adolescents with high-risk personality types (hopelessness, anxiety sensitivity, impulsivity, sensation seeking). Thirteen control schools (n= 1,103) received health education as usual. Bullying was examined for high-risk victims (n= 143 in Preventure schools versus n= 153 in control schools) and bullies (n= 63 in Preventure schools versus n= 67 in control schools) in the total sample. Harms were examined for high-risk victims (n= 110 in Preventure schools versus n= 87 in control schools) and bullies (n= 50 in Preventure schools versus n= 30 in control schools) in independent schools. There was no significant intervention effect for bullying victimization or perpetration in the total sample. In the subsample, mixed models showed greater reductions in victimization (b=-0.208, 95% CI-0.4104 to-0.002, p< .05), suicidal ideation (b=-0.130, 95% CI-0.225 to-0.034, p< .01), and emotional symptoms (b=-0.263, 95% CI-0.466 to-0.061, p< .05) among high-risk victims in Preventure versus control schools. Conduct problems (b=-0.292, 95% CI-0.554 to-0.030, p< .05) showed greater reductions among high-risk bullies in Preventure versus control schools, and suicidal ideation showed greater reductions among high-risk female bullies in Preventure versus control schools (b=-0.820, 95% CI-1.198 to-0.442, p< .001). The findings support targeting personality in bullying prevention. The CAP Study: Evaluating a Comprehensive Universal and Targeted Intervention Designed to Prevent Substance Use and Related Harms in Australian Adolescents; http://www.anzctr.org.au/; ACTRN12612000026820.