Although primaries have been popularised as the more open and participatory mechanism for selecting candidates, they often generate the opposite effect, strenghtening the personalization of politics instead of buttresing the institutionalization of parties. Our study focuses on the primaries held by the coalition of center-left (Concertación) to choose their candidates for mayor in 2012. We argue, first, that the more electoral strenght an incumbent candidate for mayor has, the less participation will be. Second, that the turnout in the general election was almost identical in communes (comunas) who held primaries and in communes who did not. Third, that primaries mainly improved the elegibility of challengers. As a consequence, primaries did not stimulate turnout but contributed to the success of candidates.