Background Medical decision-making capacity (MDC) refers to the ability to make informed decisions about treatment and declines in cognition are associated with declines in MDC across multiple disease entities. However, although it is well known that cognitive impairment is prevalent in multiple sclerosis (MS), little is known about MDC in the disease. Methods Data from 22 persons with progressive MS and 18 healthy controls were analyzed. All diagnoses were made by a board-certified neurologist with experience in MS. All study participants were administered a vignette-based measure of MDC and also a neuropsychological battery. Results Performance on three MDC consent standards (i.e., Appreciation, Reasoning, Understanding) was significantly lower for people with progressive MS as compared to healthy controls. In the progressive MS group, verbal fluency was the primary cognitive predictor for both Reasoning and Understanding consent standards. Verbal learning and memory was the primary cognitive predictor for Appreciation. MS severity was not significantly correlated with any MDC variable. Conclusion MDC is a complex and cognitively mediated functional ability that is impaired in many people with progressive MS. Verbal measures of fluency and memory are strongly associated with MDC performances in the current sample of people with MS and could potentially be utilized to quickly screen for MDC impairment in MS.