Purpose: The objective of this study was to develop and establish content validity of a new instrument titled the Military Concussion Readiness Inventory for Dizziness and Balance (MCRI-DB). The MCRI-DB was intended to recognize functional impairments and predict readiness for return-to-duty in service members who experienced mild traumatic brain injury (mTBI). Methods: Nineteen male service members were included in a nominal group technique (NGT) process to produce items for the MCRI-DB. Items were categorized according to the International Classification of Functioning, Disability and Health (ICF) and were sent to 13 physical therapy experts through a Delphi survey to determine content validity. The consensus to include an item was defined as an agreement of at least 70% of the participants. Results: The NGT produced 222 items with 108 duplicates removed. The ICF categorization linked 84 of the items to 36 unique ICF Codes, 9 items were not linkable to the ICF due to the complex nature of the activity, and 21 items were removed. After three rounds of the Delphi survey, 68 items were included in this instrument. Conclusion: In this study, we successfully combined the use of service members' experiences with expert opinion to determine content validity of the MCRI-DB. This instrument may be used for assessment of service members who have experienced mTBI to help identify environmental factors, functional activities, and body functions that may reduce the safe and efficient fulfillment of their duties and determine their ability to return-to-duty. Further research is needed to develop the psychometric properties of the instrument fully.