Background: Medical rehabilitation plays an important role in the health care of chronically ill children and adolescents. During medical rehabilitation, supporting illness‐related self‐regulation is a central goal. Beliefs about illness and beliefs about treatment are core elements of patients' self‐regulation, and there is evidence that these beliefs are relevant predictors of different health‐ and treatment‐related outcomes such as adherence. However, little is known about adolescents' beliefs about rehabilitation. This study therefore explores adolescents' treatment beliefs in the context of inpatient medical rehabilitation. Methods: A qualitative study was conducted in a German rehabilitation clinic for children and adolescents. Using a purposive sampling method, 13 adolescents (12–16 years old) were recruited. Semi‐structured, audiotaped interviews were conducted and analysed using content analysis. Results: Results demonstrate that adolescents have differentiated rehabilitation‐related treatment beliefs. Twelve themes, with various subthemes, emerged, which include access to and knowledge about rehabilitation, the rehabilitation‐related individual position and normative aspects, expectations of oneself, as well as in respect of the social context (fellow patients, contact with family and friends), expectations of the structure, process and outcome of rehabilitation, concerns and barriers and emotional aspects. Conclusions: Our explorative study revealed a broad range of rehabilitation‐related treatment beliefs in adolescents, indicating parallels, but also differences, to research results with adults. Treatment beliefs are assumed to be an influencing factor for various health‐ and treatment‐related outcomes. Thus, implications of our findings for clinical practice and further research are discussed. [ABSTRACT FROM AUTHOR]