Introduction
To examine whether an optimized intervention is a more cost-effective option than treatment as usual (TAU) for improving agitation and quality of life in nursing home residents with clinically significant agitation and dementia.

Methods
A cost-effectiveness analysis within a cluster-randomized factorial study in 69 care homes with 549 residents was conducted. Each cluster was randomized to receive either the Well-being and Health for people with Dementia (WHELD) intervention or TAU for nine months. Health and social care costs, agitation, and quality of life outcomes were evaluated.

Results
Improvements in agitation and quality of life were evident in residents allocated to the WHELD intervention group. The additional cost of the WHELD intervention was offset by the higher health and social care costs incurred by TAU group residents (mean difference, £2103; 95% confidence interval, −13 to 4219).

Discussion
The WHELD intervention has clinical and economic benefits when used in residents with clinically significant agitation.