Abstract: Objective To evaluate functional improvement following a traumatic brain injury (TBI) after admission to a postacute treatment facility, focusing on the time since injury and analysis of recovery by degree of impairment at admission. Design A retrospective study of patients who received treatment at a postacute rehabilitation facility. Setting Postacute rehabilitation for persons with acquired brain injury that involved transdisciplinary teams. Patients Patients (n = 1274) were admitted for treatment less than 5 years after TBI and were assessed on our outcome measures at least 3 times. The patients were then grouped by the time since injury and the severity of impairment at admission. Methods Patients received comprehensive multidisciplinary treatment 5 days per week, 6 hours per day. Main Outcome Measurements Function was assessed by using the Pate Environmentally Relevant Program Outcome System (PERPOS) scale at admission, discharge, and approximately every 2 weeks during treatment. By using these assessment scores, the rate and degree of improvement were monitored. Results Postacute rehabilitation yielded significant gains in functioning, with 69% of all patients who demonstrated clinically meaningful gains. The time since injury had a significant impact on gains made in rehabilitation (F time × time-since-treatment group interaction = 17.75; P P P 314 = 9.05) and moderate-to-severe (F 425 = 7.32) than for the mild-to-moderate (F 533 = 2.95) severity-at-intake groups. Conclusions Postacute rehabilitation is associated with functional gains for individuals with TBI beyond what can be explained by undirected recovery. These findings provide evidence for postacute rehabilitation as effective care after TBI.