Background <p>Acquired brain injury (ABI) includes conditions such as cerebral stroke or traumatic brain injury and is a major cause of disability. People with ABI are one of the largest groups requiring rehabilitation. Rehabilitation prognosis is an important component for goal setting and life planning. The population average prognosis (overall prognosis) and its variation describes the contextual course of health outcomes. Here, we provide the overall rehabilitation prognosis of Danish patients with moderate to severe ABI who underwent comprehensive post-acute inpatient rehabilitation.</p> Methods <p>Routinely collected electronic health record data were extracted for adults with ABI, who were admitted to a Danish highly specialised rehabilitation facility between March 2011 and December 2022. Data were deterministically linked on an individual level where necessary. The Functional Independence Measure and Early Functional Ability scale were the rehabilitation outcomes estimated across demographic and clinical candidate predictors. In addition, the probability of a missing rehabilitation outcome assessment was investigated with logistic regression models.</p> Results <p>We included 6571 rehabilitation patients. Most patients were admitted due to ischaemic (48%) and haemorrhagic stroke (16%), or traumatic brain injury (12%); approx. 40% required total assistance on admission. Patients were discharged with a median (IQR) total, motor and cognitive FIM score of 106 (67–117), 80 (47–89), and 26 (19–30), respectively. Patients improved a median (IQR) of 20 (6–40) points on the FIM, or 0.4 (0.1–0.7) points per day of rehabilitation. Persistent limitations at discharge were observed for memory and problem solving. Functional improvements were similar across ABI types. The highest likelihood of a missing rehabilitation outcome assessments was observed in patients with moderate rehabilitation needs, short rehabilitation stays and long onset-admission intervals.</p> Conclusions <p>The present study provides estimates for the overall rehabilitation prognosis for patients with moderate to high rehabilitation needs, undergoing post-acute ABI rehabilitation in a highly specialised inpatient rehabilitation facility. In our large and diverse cohort, we provide estimates for overall rehabilitation outcomes, including probabilities for missing rehabilitation outcome assessments. The provided estimates may inform future prognosis research studies in similar populations or enable comparisons with other healthcare settings.</p>