COVID-19-related school closures may have had unintended consequences affecting the ability of health professionals with school-age children to work-particularly female professionals, who often have disproportionate child care responsibilities. We combined labor-force participation data from the Current Population Survey with measures of school closures based on cell phone mobility data to examine the association between local school closures and labor supply among female nurses during the COVID-19 pandemic. During the six months after large-scale closure of schools at the end of the 2019-20 school year (March-August2020), among counties with above-median school closure rates, the employment rate of female nurses with young children declined by 12.5percentage points versus the rate during the prior four months (November2019-February2020); the change in the employment rate in below-median counties was not statistically significant. No statistically significant changes were observed among female nurses who had only older children or among male nurses. During public health emergencies, policies should consider how disruptions to schooling may affect the labor supply of health care professionals. Strategies might include direct provision of child care by health care facilities, subsidies and other aid to child care centers, or subsidies to health care workers for affordable child care.