Background: In the routine care of diabetes, mostly the clinical parameters are controlled and little attention ispaid to the quality of life assessment. A questionnaire must be culturally adapted in the country where it is intendedto be used. The aim of the study was to assess health-related quality of life in youths with type 1 diabetes using thePedsQL 3.0 Diabetes Module and to evaluate the psychometric properties in patient and control subjects.Methods: Diabetes and Generic Module were administered to 355 youths with type 1 diabetes (8-18 y/o) andtheir parents. Generic Module was completed by 294 age-matched control participants and their parents. Feasibility,internal consistency reliability, reproducibility, convergent, discriminant and concurrent validities were evaluated.Results: Minimal floor and moderate ceiling effects and hardly any missing item responses proved the feasibility.Cronbach's ? was gretaer than 0.70 in all subscales and met the criterion of 0.90 in total-items reliability. Testretestreliability was demonstrated with Pearson coefficients. We found good agreement between the children's andparents's answers, although parents underestimated their diabetic children in all subscales. The instrument was ableto differentiate between the health-related quality of life of optimal, suboptimal and high risk metabolic control. TheDiabetes Modul?? subscales and the Generic Module total scale correlated well, except the worry subscale.Conclusions: Diabetic youths had similar health-related quality of life as their non-diabetic peers. Parentsunderestimated their diabetic child's quality of life, but this was not the case in the healthy population. Both diabeticand healthy boys had better perception of quality of life than girls. The nationally adapted version of the PediatricQuality of Life Inventory 3.0 Diabetes Module designed for children and adolescents was reliable and valid instrumentfor assessing health-related quality of life in youths with type 1 diabetes