People with chronic and acute illnesses experience uncertainty about their prognoses, potential treatments, social relationships, and identity concerns. In a focus group study of people living with HIV or AIDS, we examined how social support may facilitate or interfere with the management of uncertainty about health, identity, and relationships. We found that support from others helps people with HIV or AIDS to manage uncertainty by (a) assisting with information seeking and avoiding, (b) providing instrumental support, (c) facilitating skill development, (d) giving acceptance or validation, (e) allowing ventilation, and (f) encouraging perspective shifts. Respondents also reported a variety of ways in which supportive others interfered with uncertainty management or in which seeking support imposed costs. Problems associated with social support and uncertainty management included a lack of coordination in uncertainty management assistance, the addition of relational uncertainty to illness uncertainty, and the burden of others' uncertainty management. Our study reveals strategies respondents used to manage costs and complications of receiving support, including developing an active or self-advocating orientation, reframing supportive interactions, withdrawing from nonproductive social situations, selectively allowing others to be support persons, and maintaining boundaries.