Sexual and reproductive health services are a primary reason for care seeking by female young adults, but the association of the 2010 Patient Protection and Affordable Care Act Dependent Coverage Expansion (ACA-DCE) with insurance use for these services has not been studied to our knowledge. Insurer billing practices may compromise dependent confidentiality, potentially discouraging dependents from using insurance or obtaining care. To evaluate the association between implementation of ACA-DCE and insurance use for confidential sexual and reproductive health services by female young adults newly eligible for parental coverage. For this cross-sectional study, a difference-in-differences analysis of a US national sample of commercial claims from January 1, 2007, to December 31, 2009, and January 1, 2011, to December 31, 2016, captured insurance use before and after policy implementation among female young adults aged 23 to 25 years (treatment group) who were eligible for dependent coverage compared with those aged 27 to 29 years (comparison group) who were ineligible for dependent coverage. Data were analyzed from January 2019 to February 2020. Eligibility for parental coverage under the ACA-DCE as of 2010. Probability of insurance use for contraception and Papanicolaou testing. Emergency department and well visits were included as control outcomes not sensitive to confidentiality concerns. Linear probability models adjusted for age, plan type, annual deductible, comorbidities, and state and year fixed effects, with SEs clustered at the state level. The study sample included 4 690 699 individuals (7 268 372 person-years), with 2 898 275 in the treatment group (mean [SD] age, 23.7 [0.8] years) and 1 792 424 in the comparison group (mean [SD] age; 27.9 [0.8] years). Enrollees in the treatment group were less likely to have a comorbidity (77.3% vs 72.9%) and more likely to have a high deductible plan (14.6% vs 10.1%) than enrollees in the comparison group. Implementation of the ACA-DCE was associated with a -2.9 (95% CI, -3.4 to -2.4) percentage point relative reduction in insurance use for contraception and a -3.4 (95% CI, -3.9 to -3.0) percentage point relative reduction in Papanicolaou testing in the treatment vs comparison groups. Emergency department and well visits increased 0.4 (95% CI, 0.2-0.7) and 1.7 (95% CI, 1.3-2.1) percentage points, respectively. The findings suggest that implementation of the ACA-DCE was associated with a reduction in insurance use for sexual and reproductive health services and an increase in emergency department and well health visits by female young adults newly eligible for parental coverage. Some young people who gained coverage under the expansion may not be using essential, confidential services.