Objective: To examine whether time since most recent injury and number of injuries are associated with cognitive functioning in people 55 years or older after a traumatic brain injury (TBI). Design: Observational, cross-sectional analysis. Setting: Research center at a large, urban medical center. Participants: 35 subjects with mild TBI and 28 subjects with moderate-to-severe TBI who were 6 months to 56 years postinjury. Interventions: Not applicable. Main Outcome Measures: Participants were given a neuropsychologic battery of tests that included measures of attention, processing and motor speed, language, memory, and executive functioning. Results: Multiple regression analyses indicated that processing speed, attention, and motor speed scores correlated positively with time since injury for those with moderate-to-severe injury (B range, .04−.03, P range, .007–.01). In the mild TBI group, however, time since injury was not associated with any cognitive domains of functioning. In contrast, number of injuries was unrelated to cognitive functioning in the moderate-to-severe group, whereas in the mild TBI group, number of injuries predicted attention and executive functioning scores (B range, −.40 to −.07; P range, .01–.004). Conclusions: Longer periods since injury were associated with better cognitive functioning in subjects with moderate-to-severe TBI. In people with mild TBI, on the other hand, fewer injuries were associated with better cognitive functioning. This suggests that brain plasticity may play a more significant role over time in those with severe injuries.