Objective: To evaluate the cost-utility of a lifestyle intervention among adolescents and young adults with cerebral palsy. Design: Single-blind, randomized controlled trial. Setting: Six university hospital/clinics in the Netherlands. Participants: Fifty-seven adolescents and young adults with spastic cerebral palsy classified as Gross Motor Functioning Classification System (GMFCS) level I-IV. Intervention: A 6-month lifestyle intervention consisting of physical fitness training combined with counselling sessions focusing on physical behaviour and sports participation. Main outcome measures: Data on quality of life, direct medical costs and productivity costs were collected using standardized questionnaires. Quality adjusted life years (QALYs) were derived from the Short-Form 36 questionnaire using the Short-Form 6D. Results: Quality of life remained stable over time for both groups. No significant differences between groups were found for direct medical costs or productivity costs. A cost-utility ratio of -(sic)23,664 per QALY was found for the lifestyle intervention compared with no treatment. Conclusion: The results of this study are exploratory, but indicate that implementing a lifestyle intervention for the cerebral palsy population might be cost-effective or cost-saving compared with offering no intervention to improve physical behaviour and fitness. However, the large range of uncertainty for the cost-utility ratio should be taken into account and the results interpreted with caution.