BACKGROUND: Individuals with acquired brain injury (ABI) often struggle planning and executing tasks outside daily routines. Given the pervasive effects executive functioning challenges have on independent living, professionals need methods of assessing these skills. OBJECTIVE: This study's purpose was to evaluate an ecologically-valid procedure to assess novel task planning and execution by adults with ABI. METHODS: The researchers implemented a single group design across two phases. Participants included nine adults with severe ABI. In the first experimental phase, participants created a plan for executing tasks that required adherence to pre-determined rules; in the second phase, participants executed the tasks. The researchers tallied information units recorded during the planning phase, performed momentary time-sampling to document observations about participant behaviors, and collected speed, accuracy, and rule violation data about task completion. RESULTS: Planning strategies implemented by most participants were limited to word-for-word copying of some or all of the specified tasks. On average, participants attempted and accurately performed less than half the required tasks and exhibited high rule violation rates. CONCLUSIONS: Given further development and refinement, the implemented procedures may serve as a basis for developing an ecologically-valid tool for evaluating executive functioning in adults with ABI.