Background.Xenon is a noble gas with neuroprotective properties. We previously showed that xenon improves short and long-term outcomes in young adult mice after controlled cortical impact (CCI). This is a follow-up study investigating xenon’s effect on very long-term outcome and survival. Methods.C57BL/6N (n=72) young adult male mice received single CCI or sham surgery and were treated with either xenon (75%Xe:25%O2) or control gas (75% N2:25%O2). The outcomes used were: 1) 24-hour lesion volume and neurological outcome score; 2)contextual fear-conditioning at 2 weeks and 20 months; 3) corpus callosum white matter quantification; 4) immunohistological assessment of neuroinflammation and neuronal loss; 5) long-term survival. Results.Xenon treatment significantly reduced secondary injury development (p<0.05), improved short-term vestibulomotor function (p<0.01),and prevented development of very late-onset traumatic brain injury (TBI)-related memory deficits. Xenon treatment reducedwhite matter loss in the contralateral corpus callosum and neuronal loss in the contralateral hippocampal CA1 andDG areas at 20 months. Xenon’s long-term neuroprotective effects were associated with a significant (p<0.05) reduction in neuroinflammation in multiple brain areas involved in associative memory, including reduction in reactive astrogliosis and microglial cell proliferation. Survival was improved significantly (p<0.05) in xenon-treated animals, compared to untreated animals up to 12 months after injury.Conclusions.These results show that xenon treatment after TBI results in very long-term improvements in clinically relevant outcomes and survival. Our findings support the idea that xenon treatment shortly after TBI may have long-term benefits in the treatment of brain trauma patients.