Objective: To examine the frequency and timing of inpatient engagement in meaningful activities within rehabilitation (within and outside of structured therapy times) and determine the associations between activity type, goal awareness, and patient affect. Methods: This prospective observational study performed behavioral mapping in a 42-bed inpatient brain injury rehabilitation unit by recording patient activity every 15 minutes (total 42 hours). The participants were randomly selected rehabilitation inpatients with acquired brain injury; all completed the study. The main outcome measures included patient demographics, observation of activity, participation, goal awareness, and affect. Results: The inpatients spent 61% of the therapeutic day (8:30 to 16:30) in their single room and were alone 49% of the time. They were physically socially inactive for 76% and 74% of their awake time, respectively, with neutral affect observed for about half of this time. Goal-related activities were recorded for only 25% of the inpatients’ awake time. The odds of physical activity were 10.3-fold higher among in patients receiving support to address their goals within their rehabilitation program (odds ratio=10.3; 95% confidence interval, 5.02–21.16). Conclusion Inpatients in a mixed brain injury rehabilitation unit spent a large amount of their awake hours inactive and only participated in goal-related activities for a quarter of their awake time. Rehabilitation models that increase opportunities for physical, cognitive, and social activities outside of allied health sessions are recommended to increase overall activity levels during inpatient rehabilitation.