Objectives. The effects of child care costs on the employment of single and married mothers with pre-school-aged children were analyzed. Methods. Both demographic and employment data from the March Current Population Survey were used, supplemented by child care data from various sources. Results. We find that child care costs have strong effects on employment for women with pre-school-aged children and that these effects are larger for single mothers than for married mothers. Conclusions. Our simulation results suggest that policies that reduce the costs of child care could raise the employment rate of married mothers by 3 to 14 percentage points and the employment rate of single mothers by 5 to 21 percentage points.