The Military Health System Data Repository: Leveraging Closed, Familial-Linked Electronic Health Record Data for a Large Generalizable US Population

Background: The Military Health System (MHS) Data Repository (MDR) is a large, longitudinal real-world data platform that has been used extensively in research, yet its overall structure, strengths, and limitations have not been comprehensively described for investigators outside the Department of Defense (DoD). Aims: To characterize the MDR as a fit-for-purpose real-world data source and evaluate its utility for retrospective and prospective clinical, epidemiologic, and regulatory-grade research. Materials and Methods: We performed a descriptive review of the MHS clinical ecosystem and MDR architecture, including direct care and purchased care data streams, enrollment files, structured and unstructured electronic health record content, referral data, pharmacy capture, familial linkage, and integration with DoD registries and biospecimen repositories. We also assessed population characteristics, longitudinality, and key strengths and limitations relevant to research use. Results: The MDR captures data on more than 9.5 million beneficiaries and includes decades of longitudinal information from military treatment facilities and TRICARE-financed civilian care. The repository contains comprehensive claims, enrollment, pharmacy, laboratory, radiology, clinical note, and referral data, with strong mother-child and family linkage. Its integration with resources such as the Department of Defense Serum Repository enables biomarker and pre-diagnosis studies at scale. The population is broadly generalizable to the US population across age and sex, while offering unusual advantages in pregnancy, pediatric, oncology, pharmacoepidemiology, and biosurveillance research. Discussion: Key strengths include closed-system capture, long follow-up, exceptional pharmacy data, regulatory traceability, and linkage to registries and biospecimens. Limitations include incomplete visibility into some non-TRICARE-funded care and reduced clinical granularity for privately delivered care. Conclusion: The MDR is a uniquely powerful and collaborative real-world data platform for high-impact military and civilian health research.