This study investigated the effect of severe traumatic brain injury (TBI) on prospective memory. It also sought to identify the relative contributions of executive functioning and retrospective memory to prospective memory. Thirteen patients with severe TBI and 13 matched control subjects were assessed on two novel, yet ecologically valid, experimental measures of prospective memory and standard tests of neuropsychological functioning. Participants with TBI performed significantly worse than did controls on neuropsychological tests and a time-based prospective memory task, indicating that TBI affected not only retrospective but also prospective memory functioning. Multiple regression analyses identified relationships between executive functioning and time-based prospective memory and between retrospective memory and event-based prospective memory. Implications of these findings for the assessment and rehabilitation of memory impairment in individuals with TBI are discussed.