This study aimed to analyse the impact of the disease and treatment on health-related quality of life (HRQOL) in intensively treated young patients with diabetes. Our main hypothesis was that metabolic control, gender, age and socio-economic status predict HRQOL. All children and adolescents (n = 400, 191 girls) and parents in a geographic population of two paediatric clinics in Sweden [mean age 13.2 yr, +/-SD 3.9, range 2.6-19.6; mean duration of diabetes 5.1 yr, +/-SD 3.8, range 0.3-17.6; yr mean haemoglobin A1c (HbA1c) 7.1%, +/-SD 1.2, range 4.0-10.7] received the DISABKIDS questionnaire, a validated combined chronic generic and condition-specific HRQOL measure for children, and the EuroQol-5D questionnaire. Parents as proxy perceived HRQOL lower than their children. Adolescents with separated parents reported lower generic HRQOL (GeHRQOL) and diabetes-specific HRQOL (DiHRQOL) than those with parents living together (p = 0.027 and p = 0.043, respectively). Adolescent girls reported lower GeHRQOL (p = 0.041) and DiHRQOL (p = 0.001) than boys did. Parents of girls <8 yr of age reported lower DiHRQOL (p = 0.047) than did parents of boys <8 yr. In addition, a difference was found in HRQOL between centres. Intensive insulin therapy did not seem to lower HRQOL. If anything, along with better metabolic control, it increased HRQOL. A correlation between DiHRQOL and HbA1c was found in adolescents (r = -0.16, p = 0.046) and boys aged 8-12 yr (r = -0.28, p = 0.045). We conclude that the diabetes team can influence the HRQOL of the patients as there was a centre difference and because HRQOL is influenced by glycaemic control and insulin regimen. Girls seem to need extra support.