Background and Objectives: Each year, nearly 1% of US children spend time in foster care, with 6% of US children placed in foster care at least once between their birth and 18th birthday. Although a large literature considers the consequences of foster care placement for children’s wellbeing, no study has used a nationally representative sample of US children to compare the mental and physical health of children placed in foster care to the health of children not placed in foster care. Methods: We used data from the 2011–2012 National Survey of Children’s Health, a nationally representative sample of noninstitutionalized children in the United States, and logistic regression models to compare parent-reported mental and physical health outcomes of children placed in foster care to outcomes of children not placed in foster care, children adopted from foster care, children across specific family types (eg, single-mother households), and children in economically disadvantaged families. Results: We find that children in foster care are in poor mental and physical health relative to children in the general population, children across specific family types, and children in economically disadvantaged families. Some differences are explained by adjusting for children’s demographic characteristics, and nearly all differences are explained by also adjusting for the current home environment. Additionally, children adopted from foster care, compared with children in foster care, have significantly higher odds of having some health problems. Conclusions: Children in foster care are a vulnerable population in poor health, partially as a result of their early life circumstances.