Attention-deficit/hyperactivity disorder (ADHD) is a common childhood diagnosis and affects the pool of potential military applicants. Early detection and treatment of ADHD may decrease the risk of developing comorbidities; however, accession policy in place during this study period (2014-2018) disqualified applicants who used ADHD medication for more than 24 months cumulative after age 14. The objective of this study was to assess attrition from military service in newly accessed active component service members diagnosed with ADHD as compared to controls. In addition, attrition rates and incidence rates of mental health diagnoses were assessed in service members with ADHD by treatment status (i.e., treated vs untreated ADHD) where treatment was defined as being dispensed an FDA-approved ADHD medication at least twice within 181 days. Almost two-thirds (64.8%) of newly accessed ADHD cases in 2014 were identified after enlistment medical screening at Military Entrance Processing Stations (MEPS) (i.e., post-MEPS). These post-MEPS ADHD cases accounted for 99.1% of the treated ADHD cases. The vast majority of treated cases (91.0%) were dispensed ADHD medication within 6 months of accession. The treated ADHD group had higher rates of attrition and incidence of mental health disorders during the followup period. These study findings highlight the problem of nondisclosure of ADHD among military applicants. Future changes to enlistment standards should consider the optimal way to promote applicant disclosure of ADHD during MEPS screening or for medical waiver review and should discourage withholding an ADHD diagnosis during enlistment.