DNA double-strand break repair is critical for cell viability and involves highly coordinated pathways to restore DNA integrity at the lesion. An early event during homology-dependent repair is resection of the break to generate progressively longer 3' single-strand tails that are used to identify suitable templates for repair(1). Sister chromatids provide near-perfect sequence homology and are therefore the preferred templates during homologous recombination(2,3). To provide a bias for the use of sisters as donors, cohesin-the complex that tethers sister chromatids together(4)-is recruited to the break(5,6) to enforce physical proximity. Here we show that DNA breaks promote dissociation of cohesin loaded during the previous S phase in budding yeast, and that damage-induced dissociation of cohesin requires separase, the protease that dissolves cohesion in anaphase(7). Moreover, a separase-resistant allele of the gene coding for the alpha-kleisin subunit of cohesin, Mcd1 (also known as Scc1), reduces double-strand break resection and compromises the efficiency of repair even when loaded during DNA damage. We conclude that post-replicative DNA repair involves cohesin dissociation by separase to promote accessibility to repair factors during the coordinated cellular response to restore DNA integrity.