We conducted a conversation analysis of 21 threads initiated by newcomers of an online support group (OSG) on eating disorders, to examine the discursive process of entering such a group. The analysis revealed three important issues. First, many newcomers articulate that the step to join the group is extremely difficult. Second, a presentation of the self in terms of a diagnosis works as a legitimization for joining the forum. The data suggest that participants who do not fulfil the conditions for such a legitimization do not join the forum. Third, the option of acquiring a serious symptom as a solution to the legitimization problem is offered by one of the regular members. Hence, the newcomers' discourse reveals issues relevant to the accessibility for undiagnosed sufferers. We discuss these findings theoretically as a phenomenon of self-presentation in relation to community norms. The analysis generates the hypothesis that newcomers are confronted with implicit norms regarding membership legitimacy that they should obey in their self-presentation, although they may not be ready yet to actually do so. OSGs should find strategies to facilitate various possibilities for newcomers to present themselves to the group while becoming a member. © The Author(s) 2011.