Objective: To investigate feasibility of aquatic high intensity interval training for adolescents with cerebral palsy, who can ambulate independently but may choose a mobility aid in some circumstances. Design: Pilot randomised controlled trial. Method: Following baseline assessments, participants were randomised to usual care or ten weeks of twice weekly aquatic high intensity interval training. Each class comprised 10 one-minute exercise intervals separated by one-minute rest. High intensity exercise was defined as the attainment of ⩾80% of peak heart rate measured by telemetry. Setting: Tertiary paediatric hospital. Main Measures: Primary outcomes related to the feasibility of the protocol to progress to a definitive trial. Consumer feedback was obtained. Results: Of 119 potential participants, 46 appeared eligible and 17 consented, resulting in a recruitment fraction of 37% (95% CI 23–52). Twelve completed baseline assessments and were randomised (5 males; 14 years 7 months SD 2 years 0 months). In the intervention group, of the 1190 exercise stations (across all participants and sessions), heart rate data were available for 1180 stations and high intensity exercise was achieved during 1111 stations (93%, 95% CI 92–95). All randomised participants completed the study and reported that the intervention was fun and provided friendship opportunities. There were no major adverse events or exacerbation of pain. Conclusions: Aquatic high intensity interval training in ambulant adolescents with cerebral palsy is feasible, while maintaining adherence and fidelity. Uncertainty remains on the efficacy of the intervention, highlighting the need for a large definitive trial.