Overall, having a severe mental illness diagnosis increased YPLL regardless of housing status. Homelessness was an additional and more severe contributor to YPLL, above and beyond a severe mental illness diagnosis. Thus, in this study, homelessness had the strongest effects on YPLL. However, VA patients who were not homeless and who did not have a severe mental illness diagnosis were also dying younger over time. The VA has made ending homelessness among veterans a priority, with a particular focus on those with severe mental illness. Recent VA efforts to help homeless veterans and integrate services for those with severe mental illness may have offset this trend for these vulnerable populations. Further research is needed to assess the long-term impact of emerging initiatives, such as medical home models for homeless veterans and those with severe mental illness, on reducing the mortality gap.