BackgroundObesity can significantly reduce health-related quality of life (HRQoL) and may lead to numerous health problems even in youths. This study aimed to investigate whether HRQoL varies among youths with obesity depending on grade of obesity and other factors.MethodsFor the Youths with Extreme obesity Study (YES) (2012-2014), a prospective multicenter cohort study, a baseline sample of 431 obese and extremely obese adolescents and young adults (age 14 to 24years, BMI >= 30kg/m(2)) was recruited at four German university medical centers and one job center. Obesity grade groups (OGG) were defined according to BMI (OGG I: 30-34.9kg/m(2), OGG II: 35-39.9kg/m(2), OGG III (extreme obesity): >= 40kg/m(2)). HRQoL was measured with the Euroqol-5D-3L (EQ-5D-3L), DISABKIDS chronic generic (DCGM-31) and the KINDLR obesity module. Differences between OGGs were assessed with logistic and linear regression models, adjusting for age, sex, and study center in the base model. In a second regression analysis, we included other characteristics to identify possible determinants of HRQoL.ResultsThree hundred fifty-two adolescents (mean age: 16.6 (2.4), mean BMI: 39.1 (7.5) kg/ m(2)) with available HRQoL data were analysed. HRQoL of youths in all OGGs was markedly lower than reference values of non-obese adolescents. Adjusting for age and sex, HRQoL of youths in OGG III significantly impaired compared to OGG I. Youths in OGG III were 2.15 times more likely to report problems with mobility in the EQ-5D-3L than youths in OGG I. A mean difference of 9.7 and 6.6 points between OGG III and I were found for DCGM-31 and KINDL respectively and 5.1 points between OGG II and I for DCGM-31. Including further variables into the regression models, showed that HRQoL measured by DCGM-31 was significantly different between OGGs. Otherwise, female sex and having more than 4h of daily screen time were also associated with lower HRQoL measured by DCGM-31 and KINDL.Conclusion HRQoL of adolescents with obesity is reduced, but HRQoL of adolescents with extreme obesity is particularly affected. Larger and longitudinal studies are necessary to understand the relation of extreme obesity and HRQoL, and the impact of other lifestyle or socioeconomic factors.