Objective: To examine the relationship between cognitive reserve and cognitive functioning in older adults after a traumatic brain injury (TBI). Design: Observational, cross-sectional. Setting: Research center at an urban medical hospital center. Participants: 25 subjects had mild TBI and 24 had moderate-to-severe TBI. 62 participants had no history of TBI. Interventions: Not applicable. Main Outcome Measures: Neuropsychologic battery included measures in the domains of attention, processing speed, memory, language, executive functioning, and motor ability. Results: Multiple regression analyses were used to examine Wechsler Adult Intelligence Scale–Revised (WAIS-R) vocabulary scores, and years of education both separately and combined in the Oklahoma Premorbid Intelligence Estimates (OPIE-3V). WAIS-R vocabulary predicted cognitive performance in the following domains: attention, processing speed, memory, language, and executive functioning (controls); attention, memory, and language (mild); and language (moderate to severe). Years of education and OPIE-3V did not predict higher cognitive functioning after a TBI. Conclusions: Findings suggest that performance on a vocabulary measure is a better predictor of cognitive functioning in non-TBI older adults than in those with TBI. Thus, cognitive reserve is not necessarily a protective factor for older adults with TBI. The findings also call into question the usefulness of years of education and OPIE scores as predictors of cognitive performance in older adults, as measured by vocabulary WAIS-R subtest, a more sensitive measure of premorbid intelligence than level of education.