Background Training care givers reduces their burden and improves psychosocial outcomes in care givers and patients at one year. However, the cost effectiveness of this approach has not been investigated. Objective To evaluate the cost effectiveness of caregiver training by examining health and social care costs, informal care costs, and quality adjusted life years in care givers. Design A single, blind, randomised controlled trial. Setting Stroke rehabilitation unit. Subjects 300 stroke patients and their care givers. Interventions Caregiver training in basic nursing and facilitation of personal care techniques compared with no caregiver training. Main outcome measures Health and social care costs, informal care costs, and quality adjusted life years in care givers over one year after stroke. Results Total health and social care costs over one year for patients whose care givers received training were significantly lower (mean difference -£4043 ($7249; €, 95% confidence interval -£6544 to -£1595). Inclusion of informal care costs, which were similar between the two groups, did not alter this conclusion. The cost difference was largely due to differences in length of hospital stay. The EQ-5D did not detect changes in quality adjusted life years in care givers. Conclusion Compared with no training, caregiver training during rehabilitation of patients reduced costs of care while improving overall quality of life in care givers at one year.