In 2017, the Secretary of Defense directed the Office of the Under Secretary of Defense for Personnel and Readiness to establish and maintain Department of Defense (DoD)-wide retention medical standards. As a result, the Retention Medical Standards Working Group (RMSWG) was formed. Upon publication of DoD Instruction 6130.03 Volume 2, Medical Standards for Military Service: Retention (DoDI), the RMSWG tasked the Medical Standards Analytics and Research (MSAR) team to provide advanced analytics and epidemiologic research to support these evidence-based retention medical standards. The objective of this study is to describe baseline metrics of service members (SMs) evaluated under the retention medical standards, utilizing service-specific Physical Evaluation Board (PEB) data. Between fiscal years (FYs) 2016-2021, rates of retention medical standard evaluations, using Physical Evaluation Board (PEB) records as a proxy, were relatively rare (<2% of the total force per Service). The Army (136.2 per 10,000 Soldiers) and Marine Corps (89.8 per 10,000 Marines) had substantially higher rates of retention medical standard evaluation than the Air Force (61.1 per 10,000 Airmen), and the Navy (54.2 per 10,000 Sailors). These variations may reflect any of several important inter-service differences, including but not limited to, service-specific retention evaluation processes and policies, and differing historical medical standards. The vast majority of retention evaluations involved at least one of the top 3 medical condition categories – 1. Musculoskeletal conditions (including the spine and sacroiliac joint conditions, upper extremity conditions, lower extremity conditions, generalized conditions of the musculoskeletal system subsections); 2. Behavioral health disorders; and 3. Neurological disorders. Overall, more than 90% of service members evaluated by a PEB under the retention medical standards were determined to be non-retainable and entitled to DoD disability benefits. Whether the benefit consisted of a one-time severance payment, or ongoing payments and medical care, differed substantially by the medical conditions involved, the length of time served, and several other factors. Between 1.5% (Navy) and 4% (Air Force) of evaluated service members were determined to be non-retainable and were administratively separated, while less than 3% were found fit for continued service. Median time in service prior to retention medical standard evaluation was longest among Airmen (7.7 years) and Soldiers (6.9 years) and shortest among Marines (4.0 years). These interservice differences generally align with service times in the full populations.) There was little apparent connection between medical reasons for separation and accession medical standards, as less than 10% of service members evaluated under the retention medical standards had a history of accession medical waiver, which aligns with the proportion of all military accessions who entered service via an approved medical waiver. Moreover, there was very low medical concordance between accession waiver conditions and eventual retention medical issues. MSAR is working with the services to collect additional data representing all stages of the retention medical consideration process, particularly including initial referrals by commanders or providers for review by service Medical Evaluation Boards (MEBs), and summary records from MEB evaluations.