Résumé : We aim at understanding the triggers of electoral violence, which spoiled 80% ofelections in Africa during the last decades. We focus on Burundi, a country wherepolls were organized in 2010, only few months after the end of a long-lasting civilwar. We find that an acute polarization between ex-rebels’ groups is highly conduciveto electoral violence. In particular, we predict a five-fold increase in electoralviolence between the lowest- and highest-polarized municipality. However, neitherethnic nor political cleavages significantly determine such electoral malpractices.These results are robust to numerous specifications. We therefore argue that policiessupporting the transition of ex-rebel groups from warfare to the political arenashould be reinforced.