The psychosocial effects of childhood cancer and its demanding medical treatment can affect not only the ill child but the whole family, particularly siblings who are often overlooked given the terrible circumstances these families face. Current evidence suggests that negative long-term psychosocial effects of childhood cancer may be more severe in siblings than in the child with cancer. Addressing these effects on siblings may benefit the child with cancer and the entire family. Thus, early psychosocial preventive interventions are needed to foster psychosocial adjustment in siblings and promote better quality of life for the entire family. The immediate objective of this study is to address siblings' psychological distress by assessing feasibility and efficacy of a manualized group intervention for siblings of children with cancer (Siblings Coping Together, SibCT). A longer term objective is that the evidence-based intervention could then be exported to other centres across Canada and internationally. Additionally, the study results will identify biomedical, personal, familial and social determinants of intervention outcomes that can guide clinical effort for those at greatest risk. Finally, the overall aim of the project is to reduce psychological distress and improve quality of life for siblings and families impacted by a cancer diagnosis and its demanding treatment.