One hundred twenty female undergraduates overheard an apparent accidental injury to the female E in an adjoining room. The Ss were either alone or paired; half were normally dressed, and the others were costumed and hooded as has been done in prior studies to manipulate deindividuation. The results showed that alone individuals gave aid more quickly than pairs; but, as hypothesized, deindividuated women responded more slowly than individuated women when alone and faster when in pairs. Costuming seems to activate self-consciousness which slows responding when alone, but the anonymity from the other S hastens responding in pairs, when self-consciousness is high for individuated Ss. It was concluded that costuming Ss in the effort to achieve deindividuation lessens the prospect of negative evaluation by peers when the S is called upon, either by norms or experimental demand, to act in a manner that could be damaging to the self-image—whether the action involves aiding or injuring another. Thus deindividuation in groups facilitates compliance. © 1978 Taylor & Francis Group, LLC.