Chronic fatigue syndrome or myalgic encephalomyelitis (CFS/ME) is a disabling condition known to have a negative impact on all aspects of a child's life. However, little is understood about the impact of CFS/ME on siblings. A total of 34 siblings completed questionnaires measuring depression (Hospital Anxiety and Depression Scale (HADS)), anxiety (HADS and Spence Children's Anxiety Scale (SCAS)) and European Quality-of-life-Youth (EQ-5D-Y). These scores were compared with scores from normative samples. Siblings had higher levels of anxiety on the SCAS than adolescents of the same age recruited from a normative sample; however, depression and quality-of-life were similar. Interviews were undertaken with nine siblings of children with CFS/ME who returned questionnaires. Interview data were analysed using a framework approach to thematic analysis. Siblings identified restrictions on family life, 'not knowing' and lack of communication as negative impacts on their family, and change of role/focus, emotional reactions and social stigma as negative impacts on themselves. They also described positive communication, social support and extra activities as protective factors. Paediatric services should be aware of the impact of CFS/ME on the siblings of children with CFS/ME, understand the importance of assessing paediatric CFS/ME patients within the context of their family and consider providing information for siblings about CFS/ME.