We propose a novel approach to measuring the causal effect of family structure on a child’s outcomes. In a war, some fathers are killed in action and cannot return to their families. This creates a natural experiment in which the effects of a father’s absence can be tested. Using data from the U.S. Civil War, we find no evidence that a father’s death in the war affected his child’s labor income as a young adult. We also find no effect on labor force participation or the chance of being married in 1880. Daughters of fathers who died were less likely to be students in 1880, although we find no such effect on sons.