Medical and legal professionals face the challenge of assessing capacity and competency to make medical, legal, and financial decisions in dementia patients with impaired decision-making. While such assessments have classically focused on the capacity for complex reasoning and executive functions, research in decision-making has revealed that motivational and meta-cognitive processes are also important. We first briefly review the neuropsychological literature on decision-making, as well as the medical and legal assessment of capacity. Next, we discuss the limitations of integrating findings from decision-making research into capacity assessments, including the group to individual inference problem, the unclear role of neuroimaging in capacity assessments, and the lack of capacity measures that integrate important facets of decision-making. Finally, we present several case examples where we attempt to demonstrate the potential benefits and important limitations of using decision-making research to aid in capacity determinations.