The present survey aims at determining the prevalence of extreme obesity (defined as a body mass index (BMI) ≥ 99.5th percentile) for the first time in Austria and at investigating the relationship between weight status and mother tongue in a representative Viennese sample of 24,989 children and adolescents (2-16 years) with a percentage of approximately 46 % of migration background.Directly measured anthropometric data on body weight and height were collected and BMI was calculated. Prevalence of overweight, obesity and extreme obesity was determined for every subgroup according to mother tongue using the German national reference criteria by Kromeyer-Hauschild et al.In this sample, 2.1 % of all children and adolescents had to be classified as being extremely obese. More boys (2.3 %) than girls (1.9 %) suffered from extreme obesity (p = 0.048). Total 1.7 % of children and adolescents with German as their native language, 2.5 % of Turkish native speakers and 2.9 % of children and adolescents with another mother tongue were extremely obese (p ≤ 0.001). The highest prevalence of overweight or obesity was found in Turkish-native-speaking children and adolescents (p ≤ 0.001), whereas the lowest one was found in German-native-speaking children and adolescents (p ≤ 0.001).This large study clearly shows that extreme obesity is a common disease and largely neglected. Apparently, another native language than German, as an indicator for a migration background, may be associated with a substantially higher probability for the development of extreme obesity in Vienna, Austria. Thus, effective preventive measures to overcome obesity are urgently needed.