In this paper we use records from a 19th-century Belgian community to look at mortality differences among families, or a “family effect” on mortality. We found, as in previous studies, strong evidence that child deaths tended to be clustered in some families. The situation in adulthood is more complex, however. Individuals from sibling sets with higher childhood mortality had lower mortality as adults. Higher exposure to childhood disease conferred benefits in later life, leading to longer survival in adulthood. Controlling for sibling deaths, adult mortality did differ among families, but socioeconomic differences explained part of this effect in young adulthood and all of it after age 55. These patterns are suggestive of possible explanations for the “family effect.”