Health-related quality of life is increasingly being considered as a relevant end-point and outcome criterion in evaluating the effects of medical treatment. While in adults quality of life instruments have been developed in terms of generic as well as disease-specific measures, quality of life assessment and children is a relatively new area. The current paper describes the application of a German generic quality of life instrument for children (the KINDL) in a group of 45 chronically ill children suffering from diabetes or asthma in comparison to 45 age- and gender-matched healthy children. The results of psychometric testing in these populations showed that the German KINDL is a reliable, valid and practical instrument to assess the health-related quality of life of children which should be supplemented by disease-specific modules and needs to be further tested in clinical populations.