Childhood malignancies represent the second most common cause of childhood death. In addition to affecting a child suffering from a malignant disease, this diagnosis affects the whole family, family dynamics, relationships, activities, etc. The topic of the impact of malignant disease on siblings of children with cancer has not been sufficiently investigated. Nevertheless, more and more papers are appearing on this topic precisely because the impact that this diagnosis has on these members of the closest family is increasingly recognized. Malignant disease and the situation that it leads to causes many difficult emotions in siblings such as guilt, anger, fear, but also jealousy because they often have the feeling that parents, and other members of the family and society, care more about their brother or sister with cancer, and their feelings are not taken into account. Also, the problem is the change in family dynamics that affects siblings. Separation from the brother or sister with cancer, but also from the parent who now spends time in the hospital with their brother or sister leads to feelings of rejection, but also loneliness. This thesis examines the challenges faced by siblings of children with cancer and the occurrence of stress in them due to these challenges. The thesis was written both through quantitative research conducted with the help of the Stress Scale in siblings of children with cancer. In the quantitative part of the study, 38 siblings aged 8 to 17 participated. It has been shown that siblings express strong attitudes when it comes to how to deal with the new situation and feelings related to the whole situation and their brother or sister who is being treated. It has also been shown that girls express stronger attitudes compared to boys. Qualitative methodology was also used in the research through a semi-structured interview with a young man whose sister had gotten over cancer in childhood. Significant answers related to this issue emerged that can contribute to organizing quality support for siblings of children with cancer.