Individual risk-taking often affects bystanders. We use a novel experimental approach to systematically investigate risk-taking that maximises individual but not social returns and the role of gender therein. In our experiments, individuals choose between investments in technologies that not only differ according to their level of risk and potential returns, but also by the extent to which they impose negative externalities on others. We find that both genders are less willing to take risks when they impose negative externalities. Women do not generate lower social returns on their investments than men when they act as individual investors. However, when acting in groups, we observe that women generate lower social returns than men, regardless of the gender of the other group member. These findings provide a novel view on risk-taking by men and women in the presence of risk externalities.