Eating disorders belong to the broad category of self-harming behaviours which may be acquired in a social learning process of imitation, identification and competition. Hence, we should question the possible dangers or unwanted side-effects in treating patients together within a common therapeutic setting. But little is known about the frequency and extent of possibly negative influences of treatment in a group format, the so-called risk of ‘peer contagion’ in group therapy and/or inpatient treatment. We review in this paper the rather scarce literature on this subject in order to stimulate more critical thinking and systematic research. Copyright © 2011 John Wiley & Sons, Ltd and Eating Disorders Association.