Objective: The purpose of this study is to compare health related quality of life of children and adolescents with attention deficit hyperactivity disorder (ADHD) both with health related quality of life of type 1 diabetes mellitus (T1DM) and healthy control groups. Methods: Sixty ADHD newly diagnosed cases with no treatment, age and gender matched two control groups; 60 T1DM and 60 healthy control groups aged between 8 and 16 years were enrolled in this study. The diagnostic assessments and exclusion criteria of psychiatric disorders of all subjects were made according to the DSM-IV criteria and the Kiddie-Schedule for Affective Disorders and Schizophrenia for School-Age ChildrenPresent and the Lifetime (K-SADS PL). Sociodemographic Form, Pediatric Quality of Life Scale for Children (PedsQL 4.0 TM) were applied to all of participants and their parents. DSM-IV based Turgay ADHD and Distruptive Behavior Disorders Screening Scale, ADHD Rating Scale-IV and Clinical Global Impression Scale were additionally administered to ADHD group. HbA1c levels were used in terms of T1DM disease severity. Results: Children and adolescents diagnosed ADHD reported lower self-concept in emotional functioning and psychosocial health summary scores than children and adolescents with T1DM. Compared with healthy controls, children and adolescents diagnosed ADHD reported lower self-concept in all subscales and total scores of PedsQL except physical health summary. Parent of ADHD children reported lower concept in all scores of quality of life than parents of healthy controls. Conclusions: Life quality in terms of psychosocial health were found to be impaired in newly diagnosed ADHD subjects more than T1DM and healthy controls. Evaluation of quality of life during diagnosis and treatment stages of ADHD may help to identify and manage the overall impact of the disorder. [Anadolu Psikiyatri Derg 2019; 20(5.000): 539-547]