Abstract Introduction Head injuries can be associated with hypersomnia acutely and chronically and can occur in those with mild/moderate/severe head injuries and with or without loss of consciousness. If hypersomnia persists, additional evaluation is warranted. Head injuries are increasingly reported in the military due to falls, assaults, motor vehicle accidents, and IED explosions, with some reporting, repeated blast injuries; secondary narcolepsy should be considered within the differential. Untreated narcolepsy can lead to safety issues for both the patient and others; therefore, aggressive evaluation is necessary with a PSG/MSLT combination and/or by the patient meeting the diagnostic criteria outlined in the DSM-V. Methods At the 2021 SLEEP conference, we presented a poster on our retrospective chart review of 176 patients diagnosed with narcolepsy from 2013 through 2020, with 50 patients having a history of head injury (28.4%). Of those 50 patients, nine were military veterans who reported a history of some degree of traumatic brain injury. While the majority had coexisting psychiatric disorders and/or other sleep disorders, the complaints of excessive daytime sleepiness were persistent despite aggressive treatment of the other associated diseases. The diagnosis of narcolepsy was confirmed by MSLT and/or DSM-V criteria. Results This study is a case series of 9 U.S. military veterans diagnosed with narcolepsy and a head injury history. There were eight males and one female, with the average age being 48. Five of the patients were diagnosed with type 1 narcolepsy with cataplexy, the other four without cataplexy were all on long-term treatment with antidepressants. The use of antidepressants while evaluating narcolepsy should be considered as they are REM suppressants, can interfere with MSLT findings, and can inhibit cataplexy symptoms preventing the appropriate diagnosis of Narcolepsy by DSM-V criteria. Conclusion Persistent hypersomnia in a patient with a history of a head injury could suggest a disorder of narcolepsy, and appropriate evaluation for this disorder appears indicated. The military having a high risk of head injuries may require assessment of narcolepsy while in active duty or long after discharge as the hypersomnia may be chronic and previously undiagnosed. Support (If Any) **No support was given for this research