This book outlines a range of rationales and goals for patient involvement in HTA along with a variety of methods and expected benefits. However, the benefits remain hypothetical in the absence of formal evaluation. This chapter aims to provide an overview of current practices regarding the evaluation of patient involvement in HTA. The first part posits the need for evaluating patient involvement in HTA and presents some examples of how it could impact HTA. The second part presents a review of recent scientific evidence regarding its impact. The third part discusses some requirements to assess impact and presents a framework to consider the resources, activities and results in the evaluation of patient involvement. The chapter concludes by proposing some direction and guidance to ensure rigorous evaluation of patient involvement in HTA that are adapted to the context.