A chronic illness in childhood or adolescents constitutes a drastic event for the whole family, especially for the healthy siblings. This could impair their quality of life. We designed a case-control-study in three centres (Leipzig, Giessen and Augsburg) with questionaires sent to 72 diabetic children, 71 of their siblings and 63 children of neighbourhood (controls) aged between 8 and 16 years. KINDL-Questionnaire was used for the study of the health-related quality of life of children and adolescents, supplemented by other appropriate items. The results indicate a positive health related quality of life of the healthy siblings of families with a child who has type 1 diabetes. Differences in the quality of life depend on factors such as age and gender of the children and relate to specific items of sibling relationship (e. g. "worried about sibling", "looked after sibling"). Generally, there was a great similarity with regard to the quality of life of healthy brothers and sisters from affected families compared with children of families without a child suffering from chronic illness