Using a unique dataset including all rights issues of new shares and other equity-like securities announced by Italian listed banks between 1989 and 2014, and exploiting the ideal setting provided by the Italian Banking Law, which allows for listed co-operative banks, we test if the 'one head-one vote' principle of co-operative banks and the 'one share-one vote' voting system of joint stock banks imply different agency costs of equity. Our empirical results, obtained using an event-study methodology, regressions and matching estimators, support our research hypothesis that co-operative banks have greater agency costs of equity compared to joint stock banks, and contribute to the literature on demutualization and cooperative hybrids.