Social support may be of particular importance for vulnerable adolescents' development and health and can help them to cope with stressful life events. However, knowledge of perceived social support among adolescents in Residential Youth Care (RYC) is sparse. The present study therefore aimed to investigate perceived social support among adolescents in Norwegian RYC (N = 304, mean age 16.3 years, girls 57.2%), using a short form of the Social Support Questionnaire. The results were compared with adolescents in the general population. The findings revealed that adolescents in RYC reported a lower number of support persons compared with the general population. Both populations reported a decreasing number of support persons as they aged, except for girls in RYC. The adolescents in both populations were satisfied with the support perceived, especially those with the highest number of support persons. However, social support providers differed between the two populations; RYC adolescents reported their extended family, other sources of support, and the institutional staff more often and their parents less. The findings are important for adolescents living in RYC, as knowledge of their social support network could influence the current practices and ensure contact with important support persons, affecting their development and health.