This paper reports results from a real-effort experiment in which men and women are paired to form a two-member team and asked to execute a real-effort task. Each member receive an equal share of the team's output. Workers who perform better than their partner can punish him/her by imposing a fine. We manipulate the teams' gender composition (man-man, man-woman, and woman-woman) to analyze whether an individual's performance and sanctioning behavior depends on his/her gender and the gender interaction within the team. The data show that men perform better than women but that women improve their performance if paired with women. Women sanction their partners less frequently than men do, but women are more frequently sanctioned than men. Finally, when sanctioned, women exhibit worse performance, whereas men tend to show improved performance.