Introduction: With the increased survival rates for childhood cancer, the disease is now typically viewed as a chronic rather than a terminal illness. This has resulted in changes in the impact of the disease as experienced by the whole family unit. Objectives: To investigate the psychological and behavioural effects of childhood cancer on healthy siblings of children with cancer compared with a control group. Design: An independent-group design was employed to compare the results from healthy siblings of children with cancer to a control group. Methods: Parents and healthy siblings in the oncology and control group were asked to complete questionnaires/measures regarding the psychological and behavioural functioning of the healthy siblings. Results: Healthy siblings of children with cancer were found to exhibit significantly more psychological and behavioural difficulties than children/adolescents in a control group. Age and gender of the healthy siblings were found to have a significant effect on their behavioural functioning. Parents in the oncology group were found to be more depressed than were the parents in the control group. Results are discussed in relation to previous research findings. Conclusions: Healthy siblings of children with cancer and their parents were at an increased risk of experiencing psychological and behavioural problems compared to a control group. Clinical implications, in light of these findings, are discussed. Strengths and limitations of the present study are addressed and areas for future research are explored.