To assess Belgian siblings’ self-reported quality of life (QoL) and the impact of illness on four different paediatric illnesses. Healthy siblings (n = 131) of children with type 1 diabetes, cancer, congenital heart disease (CHD) and cystic fibrosis (CF) completed the Child Health Questionnaire and the Sibling Perception Questionnaire. Results were compared to those of a matched group of siblings of healthy children. Siblings reported a good QoL, similar to controls, with the exception that siblings reported better on the QoL domain pain (p < .01). QoL was not related to time since diagnosis but the impact of illness was higher nearer to the time of diagnosis (r = -.39, p < .001). QoL of siblings of children with CHD or cancer was lower than QoL in the CF or type 1 diabetes group whilst impact of illness was highest for the CHD group. QoL of siblings of a child with a chronic illness is similar to the QoL of peers. Studies investigating siblings’ QoL or the impact of illness on siblings should include the day-to-day demands of the illness as well as less obvious illness-related issues like ‘hidden stress’ and ‘sense of control’.