Background: The aim of the present study is to describe the quality of life (QoL) of siblings of children with cancer and to predict it according to their health before the diagnosis of cancer in the ill child and their ways of coping with the illness. Methods: Participants were 83 siblings from 56 families - 46 girls and 37 boys, aged 7-18. The assessment took place 1 month to 8 weeks after the diagnosis of cancer in the ill child. The siblings' QoL was assessed with the TNO-AZL children's quality of life questionnaire (TACQOL). Coping strategies were assessed with the Cognitive Coping Strategies Scale for siblings (CCSS-s). Physical problems and eating and sleeping problems that existed before the ill child was diagnosed were determined in a structured interview with the parents. Results: A substantial number of siblings reported impaired cognitive and emotional QoL compared to the reference group. School-aged siblings (7-11 years) reported more trouble with motor functioning than peers. The coping strategy 'predictive control' (maintaining positive expectations regarding the illness) positively predicted siblings' QoL. The presence of health problems before diagnosis was negatively associated with siblings' QoL. Older siblings reported more negative emotions, while girls reported lower social QoL and reliance on 'interpretative control' (trying to understand the illness) was associated with fewer positive emotions. Conclusions: During the first 2 months after the diagnosis of cancer in a brother or sister, siblings have relatively lower QoL than peers. Health problems that existed before diagnosis may be a predictor of later adjustment problems. Positive expectations about the course of the illness appear to protect siblings from distress. Information about the illness is a delicate issue that requires parental guidance.