PURPOSE: We examined prospective associations between early childcare precarity, or the security and reliability of childcare arrangements, and subsequent maternal health. STUDY DESIGN: We conducted a secondary analysis of survey responses from mothers of 2,836 children in the Future of Families and Child Wellbeing study. We assessed the following childcare measures: insecure childcare, insecure childcare with missed work, inadequate childcare, and emergency childcare support. We used linear and logistic regression models with robust standard errors to examine associations between these measures when the index child was age 3 and maternal health outcomes (overall health, depression, and parenting stress) later when the child was age 9. We then examined additive experiences of childcare measures across child ages 1 and 3 on maternal health outcomes. RESULTS: Early inadequate childcare was associated with higher odds of later poor maternal overall health (adjusted odds ratio [aOR], 1.64; 95% confidence interval [CI], 1.11-2.41). All early childcare precarity measures were associated with higher odds of maternal depression (insecure childcare [aOR, 1.64; 95% CI, 1.23-2.18]; insecure childcare with missed work [aOR, 1.58; 95% CI, 1.13-2.22]; and inadequate childcare [aOR, 1.75; 95% CI, 1.22-2.51]). Emergency childcare support was associated with lower odds of adverse maternal health outcomes (poor overall health [aOR, 0.65; 95% CI, 0.48 to 0.88]; depression [aOR, 0.73; 95% CI, 0.54 to 0.99]; and parenting stress [B -0.45; 95% CI, -0.80 to -0.10]). Prolonged experiences had stronger associations with maternal health than shorter experiences. CONCLUSION: Early childcare precarity has long-term adverse associations with maternal health, and emergency childcare support seems to be favorable for maternal health. These findings highlight childcare precarity as a social determinant of women's health for researchers, clinicians, and decision-makers.