Peer relations and close friendships play important roles in youngsters' emotional development and take on special significance when a child or adolescent has a chronic disease. This article reviews the key ways that peer relations have been examined in youth with chronic pediatric conditions and specifically focuses on (1) the role of peers and close friends as a source of support, (2) friends' influence on treatment adherence, and (3) peers' and friends' impact on health-promoting and health-risk behaviors. In general, youngsters with chronic conditions do not have more problems in their peer relations than other youth, although children with medical conditions that are stigmatizing or that involve the central nervous system (CNS) may encounter peer difficulties. Social support from friends and classmates appears to facilitate youngsters' disease adaptation and may help with the lifestyle aspects of treatment regimens. Adolescent peer-crowd affiliations (e.g., "brains," "jocks") that are linked with health-promoting behaviors may prove beneficial to youngsters' disease management and health. The findings underscore the need for helping children and adolescents disclose their medical condition to peers in positive ways and for including youngsters' close friends in the treatment process and in school-reentry programs after extended medical care. Additional research is needed to develop strategies for incorporating youngsters' peers and friends into the medical management of youth with chronic pediatric conditions.