Childhood obesity has reached an epidemic level in both developed and developing countries^{(Reference Sahoo, Sahoo and Choudhury1)}. Obesity has a major impact on children's and adolescents' health and wellbeing^{(Reference Sahoo, Sahoo and Choudhury1,Reference Lakshman, Elks and Ong2)} . Weight stigma in children and adolescents is often experienced in bullying, victimization and teasing at school, home and other places^{(Reference Pont, Puhl and Cook3)}. Weight stigma linked to obesity is associated with adverse physical and psychological outcomes that undermine the prevention and treatment of obesity^{(Reference Guardabassi, Mirisola and Tomasetto4,Reference Papadopoulos and Brennan5)} . The present study aims to explore knowledge and perceptions of obesity and weight stigma in adolescents. A mixed-method study using an online questionnaire and a phone interview to explore knowledge and perceptions of obesity and weight stigma in adolescents (14–18years). Participants who agreed to participate in the phone interview were contacted, and recruitment stopped when saturation of themes was reached. Descriptive analysis (of multiple choices and Likert scales) was used to assess sociodemographic data, obesity knowledge, and perception of obesity management using SPSS (Version 28). Inductive thematic analysis following a socioecological model was used to analyse the qualitative data from the phone interviews using Nvivo (Version 12Pro). The mean (SD) age of participants (n = 686) was 16 (±1.4) years, 61% were males, and 69% were White British. Participants self-reported their weight and height, and more than half (67%) had overweight or obesity. Most of the participants (n = 529, 78%) identified obesity as a disease, 33% defined obesity as a high body fat percentage, while 7% stated they didn't know or weren't sure what obesity is. Around a third (n = 214, 28%) of those who experienced weight stigma (40%) said it was harsh. Moreover, 59% said they mainly experienced weight stigma at local community places (i.e., school clubs, extracurricular activities). Forty-one percent believed that the best weight management tool is the combination of a healthy diet and exercise, while only (9%) recommended weight loss medications. Eleven participants were interviewed. Almost all interviewed participants (n = 10) were aware of obesity and weight stigma as an issue affecting children and adolescents with overweight and obesity. Ten interviewed participants linked obesity to food and diet and recommended a balanced/healthy diet to prevent obesity. Six participants recommended avoiding junk food, sugar and fat. Six participants were weight stigmatised. Weight stigma made participants feel anxious and humiliated. The majority of participants believed obesity is a medical condition. Almost all interviewed participants were aware that weight stigma is a problematic issue, and more than half experienced weight stigma. A healthy diet and exercise regimen is believed to be among the best weight management tools.