Background: Multiculturalism has been purported to be supportive of positive youth development and outcomes. This study examined the relationship between perceived school multiculturalism--whether youth felt and thought that their school and teachers supported and provided activities for diverse intergroup interactions--and serious interpersonal violence, and explored whether this relation was mediated by civic engagement, ethnic identity, ethnocultural empathy, and positive peers. Methods: An ethnically diverse sample of 324 middle-school youth (mean age: 12.5 years; range: 11-15 years; sex: 50% female) from a city in northern California participated in the study. Analyses consisted of structural equation modeling with bootstrapping. Results: The results revealed a negative association between school multiculturalism and interpersonal violence that was fully mediated by positive peers and civic engagement. Although school multiculturalism was positively associated with ethnic identity, ethnic identity, in turn, was not significantly associated with interpersonal violence. Conclusions: School multiculturalism is an important protective factor against youth violence by facilitating positive peer relationships and community engagement among youth. Teachers, administrators, and health officials need to consider the ways in which they can facilitate and encourage greater understanding, openness, and respect for diversity, and promote harmonious interactions among different groups at schools. Greater institutional support for school multiculturalism through implementation of tolerance curriculum and activities, for example, could in turn facilitate favorable youth outcomes. (Contains 2 tables and 1 figure.)