This study examines the relation between risk exposures in early life and hazard of mortality among 11,978 Union Army veterans aged 50 and over in 1900. Veterans' risk exposures prior to enlistment—as approximated by birth season, country of birth, residential region, city size, and height at enlistment—significantly influenced their chance of survival after 1900. These effects are robust irrespective of whether socioeconomic well-being in 1900 has been taken into account; however, they are sensitive to the particular age periods selected for survival analysis. Whereas some of the effects such as being born in Ireland and coming from large cities became apparent in the first decade after 1900 and then dissipated over time, the effects of birth season, being born in Germany, residential region in the United States, and height at enlistment were more salient in the post-1910 periods. Height at enlistment shows a positive association with risk of mortality in the post-1910 periods. Compared to corresponding findings from more recent cohorts, the exceptional robustness of the effects of risk exposures prior to enlistment on old-age mortality among the veterans highlights the harshness of living conditions early in their lives.