Introduction: Stress fractures are common among military trainees due to physically demanding activities during Initial Entry Training (IET). Stress fractures result in increased morbidity and long-term absence from training and/or medical invalidity for the individual. One systemic review reported basic training stress fracture rates between 0.9%-5.2% (males) and 3.4%-21.0% (females)1. Musculoskeletal injuries contributed to nearly 70% of medical discharges across the Army from 2011 through 2016 and over 90% of medical disability discharges within enlisted Soldiers’ first year of Military Service Obligation (MSO) from 2010 to 20152. While previous data shows musculoskeletal injuries account for many medical separations in the first year of enlistment, no prior studies have examined the relationship of Lower Extremity Stress Fracture (LESFX) and separation from military service during Initial Enlistment Contract (IEC). We hypothesized that LESFXs sustained during IET and IEC would be associated with a higher risk of separation prior to MSO completion than those Soldiers without LESFXs. Methods: This is a retrospective, observational study utilizing data from the Medical Assessment and Readiness System (MARS) at Womack Army Medical Center, Ft. Bragg. We examined U.S. Army Soldiers who sustained LESFX during their first and second service years. We investigated if these Soldiers experienced higher rates of separation from military service (medical and all-cause) prior to completion of IEC and/or within the first three MSO years. Results: We observed 537,478 Soldiers entering Active Duty between 2016-present for 14,020,519 total observation months (Mean: 26.1±12.8; range 1-36). 28,358 suffered a LESFX. The majority of which, 92.2% (n=26,131) occurred within the first year of service. We observed 1,303 (0.2%) total disability separations in this population. Those with LESFX were more likely to experience disability separation (LESFX: n=163; 0.6%; No LESFX: n=1,140; 0.2%; χ²=136.7; P<0.001). Soldiers with LESFX served an average of 3.2 months less of their MSO than those without LESFX. Those diagnosed in the first year served 10.6 months less than those diagnosed with LESFX during the second year of service (n=1,426; 5.0%). Soldiers with LESFX in the second year of service were more likely to receive a disability separation within the first 36 months compared to those with LESFX in the first service year (Year 1: n=144; 0.6%; Year 2: n=17, 1.2%; χ²=9.6; P=0.002). Conclusion/Discussion: LESFX diagnoses within the first two MSO years were associated with decreased Soldier retention. Soldiers with any LESFX were more likely to separate for disability than those without LESFX.LESFX timing affected Active-Duty service term length, as Soldiers with LESFX in the first year served less Active-Duty time and were less likely to complete their IEC. LESFX during initial service commitment were associated with increased risk of early military service separation, impacting current and projected force readiness. The secondary effects of these injuries impact manning capabilities, readiness metrics, and financial losses to the organization. Future studies should focus on reducing the risk of LESFXs among new recruits to identify factors to maintain force generation and increase post-injury retention.