Introduction: Cognitive dysfunction is common in progressive supranuclear palsy (PSP) but its effect on medical decision-making has not been well studied. To address this gap in the research literature, we compared the medical decision-making capacity of patients with PSP to groups of patients with other neurodegenerative disorders. We also investigated the cognitive correlates of medical decision-making in our PSP sample. Methods: The sample was composed of 65 participants that belonged to five study groups: 13 with PSP, 13 with PD-MCI, 13 with PDD, 13 with AD, and 13 cognitively healthy controls. A neuropsychological battery, including a performance-based measure of medical decision-making capacity, was administered to all study participants. Results: Over 80% of the PSP group exhibited impairment in some aspect of medical decision-making and rates of impairment in PSP were similar to PDD. A number of cognitive abilities contributed to medical decision-making impairment in the PSP group, with executive function and attention being primary contributors. Medical decision-making was not associated with either disease duration or severity. Conclusions: Impaired medical decision-making appears to be a prevalent feature of PSP and impairments in specific cognitive domains may negatively affect the ability of this cohort to make sound medical decisions. The cognition of patients with PSP has likely declined to the point of affecting decision-making ability at the time of diagnosis and recruitment to research studies. This finding has important implications about the ability of clinicians and researchers to consent patients with PSP for research or treatment.