The Affordable Care Act–dependent coverage expansion provision implemented in 2010 allows young adults to be covered under their parents’ health insurance until age 26 years, and millions of young adults have gained insurance as a result. The impact of this policy on cancer patients has yet to be determined. Using 2007 to 2012 data from 18 registries of the Surveillance, Epidemiology, and End Results Program, comparing cancer patients age 19 to 25 years to a control group of patients age 26 to 34 years who were not affected by the provision, we observed a 2.0 (95% confidence interval [CI] = 0.7 to 3.4) percentage point decrease in uninsured rate and a 2.7 (95% CI = 0.6 to 4.8) percentage point increase in diagnosis at stage I disease for patients age 19-25 years. Further analyses by specific cancer site revealed that the statistically significant shifts were confined to carcinoma of cervix (21.2, 95% CI = 9.6 to 32.7 percentage points) and osseous and chondromatous neoplasms (14.4, 95% CI = 0.3 to 28.5 percentage points), which are detectable by either screening or clinical manifestation. These early observations suggest the policy has had positive benefits in cancer outcomes.