OBJECTIVE: Due to the unique importance of parental and sibling relationships and concurrently existing developmental challenges, the loss of a parent or sibling due to cancer is a highly stressful event for children and adolescents. This is the first systematic review that integrates findings on psychosocial outcomes after parental or sibling cancer bereavement. METHODS: A systematic search of Web of Science, PubMed, PsycINFO, and PubPsych was conducted, last in December 2017. Quantitative studies on psychosocial outcomes of children and adolescents who lost a parent or sibling due to cancer were included. RESULTS: Twenty-four studies (N = 10 parental and N = 14 sibling bereavement), based on 13 projects, were included. Ten projects had cross-sectional designs. Only 2 projects used large, population-based samples and nonbereaved comparison groups. Outcomes were partially measured by single-item questions. Bereaved children and adolescents showed similar levels of depression and anxiety compared with nonbereaved or norms. Severe behavioral problems were found rarely. However, in 2 large, population-based studies, about half of the bereaved individuals reported unresolved grief. Bereaved adolescents had a higher risk for self-injury compared with the general population in one large, population-based study. Communication with health-care professionals, family, and other people; social support; distress during illness; age; gender; and time because loss were associated with psychosocial bereavement outcomes. CONCLUSIONS: Results indicate a high level of adjustment in cancer-bereaved children and adolescents. A modifiable risk factor for adverse psychosocial consequences is poor communication. Prospective designs, representative samples, and validated instruments, eg, for prolonged grief, are suggested for future research.