Abstract Objective While there are several studies on children’s and adolescents’ beliefs about illness and medication treatment, there is limited research on their treatment beliefs in the context of rehabilitation. The Rehabilitation Treatment Beliefs Questionnaire (RTBQ) was the first instrument available to assess pediatric patients’ rehabilitation-related treatment beliefs. However, the RTBQ had some limitations that we aimed to address in this study: We revised the content of the RTBQ to include previously unaddressed dimensions of rehabilitation-related treatment beliefs, and we thoroughly tested its psychometric properties based on a sizeable, multicenter sample of adolescents with different chronic diseases. Methods Across 11 pediatric rehabilitation clinics throughout Germany, eligible patients aged 12–18 years with any chronic physical or mental health condition were invited to participate in an online survey. Psychometric evaluation included item analysis, exploratory factor analysis, internal consistency and construct validity. Results The sample comprised N = 294 adolescents (M = 14.2 years) with various chronic conditions. Psychometric testing demonstrated a coherent factor structure with 6 interpretable scales covering process and outcome expectations, expectations of one’s own role in the treatment process, structural expectations, concerns, and emotions, the latter three representing previously unaddressed dimensions of rehabilitation-related treatment beliefs. Internal consistency was acceptable to good. Construct validity analyses showed mostly hypotheses-consistent correlations with related constructs. Conclusions The revised RTBQ provides a psychometrically well-tested, adolescent-specific, and disease-generic instrument that captures multiple dimensions of rehabilitation-related treatment beliefs. Practical implications include identifying adolescents’ beliefs about rehabilitation treatment in order to actively involve them in their illness management.