Objective: To identify cognitive predictors of medical decision-making capacity (MDC) in participants with moderate to severe traumatic brain injury (TBI). Participants: At baseline, participants were 34 adults with TBI and 20 healthy adults. At 6-month follow-up, participants were 24 adults with TBI and 20 healthy adults. Main Outcome Measures: Participants were administered the Capacity to Consent to Treatment Instrument (CCTI) and neuropsychological test measures. Multivariate cognitive predictor models were developed for CCTI consent abilities/standards (S) of understanding (S5); reasoning (S4); and appreciation (S3). Results: At baseline, short-term verbal memory and semantic fluency predicted TBI group performance on understanding (S5); short-term verbal memory and attention predicted performance on reasoning (S4); and working memory predicted performance on appreciation (S3). At 6 month follow-up, executive function, verbal processing speed, and working memory predicted TBI performance on understanding (S5); working memory and short-term memory predicted reasoning (S4); and basic executive functioning predicted appreciation (S3). Conclusions: Multiple cognitive functions are associated with acute impairment and partial recovery of MDC in patients with TBI. Short-term verbal memory predicted consent capacity of TBI participants at the time of acute inpatient hospitalization, while executive functioning and working memory predicted improved capacity at six-month follow-up. © 2008 American Psychological Association.