Three studies tested the hypothesis that an individual acting alone, compared with an individual group member, would be held more responsible for behavior leading to a negative consequence. In one study, 240 subjects read scenarios of an event with a negative outcome involving one, two, three, or four individuals. As predicted, there was a significant inverse relationship between the number of participants and the degree of attributed responsibility. The second study investigated subjects’ attributions of responsibility for criminals committing a crime alone or with a partner. Single perpetrators were considered more responsible than those acting with a partner, although there was no difference in sentence length assigned. In the third, archival-type study, prison sentences for criminals who had actually committed a robbery alone or with others were examined. Again, there was diffusion of responsibility: criminals acting alone received significantly longer sentences than perpetrators who had committed a similar crime, but who had acted with others.