Social dilemmas often impose negative externalities on third parties. We experimentally analyze gender differences in cooperation in such a setting, i.e., a prisoner's dilemma game, with a passive third party that may be harmed when active players mutually cooperate. Applying a within-subjects setting, we compare cooperation under anonymity and social information, as personal characteristics are commonly known in real-life relations. Results show that the presence of a negative externality particularly affects guilt-averse women, who cooperate less often independently of the degree of information they receive. No gender difference is found absent negative externalities.