Background A third of children in England are overweight or obese (body-mass index >25 kg/m2). Current guidance from the National Institute for Health and Care Excellence recommends that obese adolescents attend a family-based multicomponent lifestyle weight management programme. However, these programmes have low recruitment and high rates of attrition. An understanding of the opinions of adolescents is necessary for planning and developing future interventions. The aim of this systematic review was to explore the viewpoints of overweight–obese adolescents who have attended a lifestyle obesity treatment intervention. Methods Studies of overweight–obese adolescents (aged 12–17 years) who attended a single or multicomponent lifestyle treatment intervention were examined. Only studies that collected and analysed data qualitatively were included. There were no language restrictions. Published literature was identified by searching the following databases: Medline, EMBASE, Web of Science, PsycINFO, ASSIA, and CINAHL between July 27 and 31, 2016. Search terms included obesity, overweight, views, experiences, opinions, attitudes, satisfaction, preferences, adolescents, diet, activity, and behaviour. Reference lists of included studies were screened. Titles and abstracts of identified records were assessed independently by two reviewers. Full texts of all potentially relevant papers were retrieved and assessed independently by two reviewers, reasons for exclusion were recorded, and differences in opinions were resolved by a third reviewer. Methodological quality was assessed by two reviewers independently, in terms of trustworthiness and usefulness of findings, with an EPPI-Centre tool. Full texts were analysed with thematic synthesis. The Confidence in the Evidence from Reviews of Qualitative research approach was used to assess the certainty of review findings. This study is registered with PROSPERO, number CRD42016039588. Findings 19 230 records were identified for title and abstract screening. 284 full -texts were assessed, with 24 included. Thematic synthesis resulted in 178 descriptive codes, which led to the development of 43 analytical themes that have been broadly divided into eight sections: support, motivations, intervention content, maintenance, diet, technology, barriers, and physical activity. Analytical themes included “professional support valued”, “tailored intervention”, “adolescents enjoy using technology and do so with ease”, “prior fears of attending intervention”, “enjoyment of sport and physical activity”, and “longer term support”. Interpretation Our findings may inform local and national policy makers in the development of future interventions for overweight–obese adolescents. Developing interventions with adolescents' opinions in mind, might assist in the improvement of recruitment and attrition rates.