People are less likely to make moral decisions when they are in groups. I study when this phenomenon makes groups less likely to produce a morally desirable outcome than one individual alone. I formulate and test a model in which a moral outcome occurs if at least one individual makes a costly decision. Using a lab experiment and data from field experiments on the bystander effect, I show that if most individuals are moral, the moral outcome is more likely to be produced by one individual, whereas if most individuals are immoral, it is more likely to be produced by a group. This rule is not only useful for reconciling previous mixed evidence on moral decisions in groups, but may also be applied to better design organizations and institutions.