The paper presents the first psychometric and content analysis results of the German KINDL questionnaire, a generic quality of life instrument for children. It was applied to 45 chronically ill children (diabetes or asthma) and compared to 45 healthy children. The results showed that the German KINDL is reliable, valid, and practical for assessing children's health-related quality of life. It should be supplemented with disease-specific modules and further tested in clinical populations. The paper discusses the importance of quality of life in children, highlighting the need for instruments that assess both physical and emotional aspects. Despite the growing interest in quality of life research, only 13% of publications focus on children. The paper reviews existing instruments and highlights the need for child-centered approaches. It describes three approaches to quality of life assessment: clinical rating, utility-based, and psychometric. The KINDL was developed based on a conceptual model and includes four components: psychological well-being, social relationships, physical function, and everyday life activities. It consists of 40 items, scored from 1 to 5, and has shown good reliability and validity. The KINDL has been used in various studies, including a longitudinal public health study and clinical trials. The paper concludes that the KINDL is a useful tool for assessing children's quality of life but needs further validation in chronically ill populations. The study aimed to evaluate the KINDL in chronically ill children and address the research questions of its validity and reliability in this population.The paper presents the first psychometric and content analysis results of the German KINDL questionnaire, a generic quality of life instrument for children. It was applied to 45 chronically ill children (diabetes or asthma) and compared to 45 healthy children. The results showed that the German KINDL is reliable, valid, and practical for assessing children's health-related quality of life. It should be supplemented with disease-specific modules and further tested in clinical populations. The paper discusses the importance of quality of life in children, highlighting the need for instruments that assess both physical and emotional aspects. Despite the growing interest in quality of life research, only 13% of publications focus on children. The paper reviews existing instruments and highlights the need for child-centered approaches. It describes three approaches to quality of life assessment: clinical rating, utility-based, and psychometric. The KINDL was developed based on a conceptual model and includes four components: psychological well-being, social relationships, physical function, and everyday life activities. It consists of 40 items, scored from 1 to 5, and has shown good reliability and validity. The KINDL has been used in various studies, including a longitudinal public health study and clinical trials. The paper concludes that the KINDL is a useful tool for assessing children's quality of life but needs further validation in chronically ill populations. The study aimed to evaluate the KINDL in chronically ill children and address the research questions of its validity and reliability in this population.