Memory deficits are among the most common chronic and functionally important consequences of traumatic brain injury (TBI). Basic and clinical research studies suggest that persistent deficits in verbal memory are associated with chronically reduced levels of acetylcholine in the brain. Medicines that increase levels of acetylcholine in the brain appear to improve memory and other cognitive problems experienced by persons with TBI. However, the studies performed thus far do not provide the level of evidence needed to establish best practices. This study will definitively establish whether, and to what extent, donepezil is an effective treatment for functionally important TBI-related memory deficit.