While there is ample evidence of a society-wide cooperation norm, it is not as clear who upholds this norm. In the present paper, we investigate whether there are gender differences with respect to norm enforcement. We let 1403 subjects play games of punishment and reward, individually or in groups with varying gender composition. Broadly, the results indicate that there are no clear gender differences: men are about as inclined as women to punish norm-breakers. However, behavior is context-dependent: men acting among other men are less inclined to uphold a cooperation norm than are women, or men in gender-mixed groups.