The Patient Protection and Affordable Care Act (ACA) included provisions to extend dependent health care coverage up to the age of 26 years in 2010. The authors examined the early impact of the ACA (before the implementation of insurance exchanges in 2014) on insurance rates in young adults with cancer, a historically underinsured group.Using National Cancer Institute Surveillance, Epidemiology, and End Results data for 18 cancer registries, the authors examined insurance rates before (pre) (January 2007-September 2010) versus after (post) (October 2010-December 2012) dependent insurance provisions among young adults aged 18 to 29 years when diagnosed with cancer during 2007 through 2012. Using multivariate generalized mixed effect models, the authors conducted difference-in-differences analysis to examine changes in overall and Medicaid insurance after the ACA among young adults who were eligible (those aged 18-25 years) and ineligible (those aged 26-29 years) for policy changes.Among 39,632 young adult cancer survivors, the authors found an increase in overall insurance rates in those aged 18 to 25 years after the dependent provisions (83.5% for pre-ACA vs 85.4% for post-ACA; P<.01), but not among individuals aged 26 to 29 years (83.4% for pre-ACA vs 82.9% for post-ACA; P = .38). After adjusting for patient sociodemographics and cancer characteristics, the authors found that those aged 18 to 25 years had a 3.1% increase in being insured compared with individuals aged 26 to 29 years (P<.01); however, there were no significant changes noted in Medicaid enrollment (P = .17).The findings of the current study identify an increase in insurance rates for young adults aged 18 to 25 years compared with those aged 26 to 29 years (1.9% vs -0.5%) that was not due to increases in Medicaid enrollment, thereby demonstrating a positive impact of the ACA dependent care provisions on insurance rates in this population. Cancer 2016;122:1766-73. © 2016 American Cancer Society.