Importance: In 2011, over 250,000 children were placed in foster care. These children are a vulnerable population suffering not only high rates of mortality, but also high rates of physical and mental health problems as a result of a history of maltreatment and living arrangement instability, yet it is unknown how many children will ever be placed in foster care.

Objective: To estimate what percentage of U.S. children will ever be placed in foster care by age 18, as well as how this percentage varies by year (2000-2011) and child sex and race/ethnicity.

Design, Setting, and Participants: Synthetic cohort (also known as period) life tables were used. Participants were all children in the Adoption and Foster Care Analysis and Reporting System (AFCARS) data, which includes all children ever placed in foster care since 2000.

Main Outcome Measure: Having ever been placed in foster care by age 18.

Results: Between 2000 and 2011, the percentage of all U.S. children estimated to ever be placed in foster care by age 18 ranged from 4.76% to 5.91%. Native American (10.54% to 15.44%) and Black (8.84% to 11.53%) children were more likely to ever be placed in foster care than were Hispanic (4.33% to 5.35%), White (3.82% to 4.86%), and Asian (1.41% to 2.61%) children. Sex differences in the cumulative risk of foster care placement by age 18 were negligible.

Conclusions and Relevance: Having ever spent time in foster care is more common than often thought, especially for Black and Native American children. Medical professionals working with these communities should consider screening for a history of foster care placement in order to improve their understanding of the childhood risk factors their patients have been exposed to.