Purpose: To assess metabolic function among adolescent and young adult (AYA) survivors of childhood cancer-related brain surgery or cranial irradiation (CRT) and to determine feasibility, safety, and metabolic as well as psychological impact of a 6-month exercise program in this cohort. Methods: Twenty AYAs aged 15-23 years were recruited. All had completed cancer treatment by age 15.5 and were more than 1 year after end of treatment. Metabolic function was assessed at baseline (T1), after a 6-month non-intervention period (T2), and after the 6-month intervention (T3). Psychological assessments were performed at T1 and T3. Eight to 12 months after the program (T4), its lasting impact was assessed by questionnaire. The 6-month intervention consisted of small group-based, tailored, supervised exercise sessions combining resistance and aerobic exercise. Sessions were offered up to thrice per week and adherence defined as participation in ≥24 sessions. Flexibility was built into the design with an alternative home-based program offered to those who could not attend the gymnasium. Results: Thirteen of the 20 recruited participants were adherent to the program. There was one fall during exercise, but no injury was sustained. Higher rates of metabolic impairment than would be expected in a healthy cohort were found at baseline both among brain tumor survivors and survivors of total body irradiation. Central adiposity reduced post-intervention (p = 0.014) and improvements in adaptive function were seen. Participants enjoyed the program, but work and study commitments limited attendance. Conclusion: AYA survivors of childhood brain tumors and CRT should be screened for metabolic and psychological well-being. Small group-based exercise is safe, feasible, and enjoyable for this cohort and may benefit them both metabolically and psychologically. Trial registration: ACTRN12614000796684. Retrospectively registered July 28, 2014.