Background: Disparities in young adult cancer survival between individuals with Medicaid and private insurance have been reported. To further understand the association between insurance-related access to healthcare and young adult cancer survival, we used Surveillance, Epidemiology, and End Results (SEER)-Medicaid linked data to test two hypotheses: 1) Those linked to Medicaid have lower cancer survival than those not linked, and 2) those with discontinuous enrollment in Medicaid around the time of diagnosis have lower survival than those with continuous enrollment. Methods: SEER-Medicaid linked data from 2006 to 2013 were obtained. Follow-up for vital status was through 2018. We included individuals diagnosed with a first malignant primary cancer diagnosed between 20 to 39 years. We excluded individuals who were linked to Medicaid enrollment records in multiple states during the same year. Individuals were defined as Medicaid-linked if they were linked to Medicaid in any U.S. state or the District of Columbia from 2006 to 2013. Medicaid enrollment was classified as continuous (enrolled within both the three months before and after diagnosis) and discontinuous (enrolled only within the 3 months before or after diagnosis or only at diagnosis). We used survival analysis methods including Kaplan-Meier (KM) curves and Cox Proportional Hazards (PH) regression models to evaluate survival differences in association with Medicaid linkage and enrollment timing after adjusting for race and a measure of census tract poverty. Results: Our analytic dataset included 137,259 young adults, among which there were 22,955 cancer deaths. KM curves showed consistently lower survival probabilities over time in young adults who linked vs. those not linked to Medicaid and in those with discontinuous vs. continuous enrollment (p < .0001). Adjusted Cox PH regression models indicated that those who linked to Medicaid had a 2.19 (95% CI 2.14-2.25) times higher hazard of death vs. those who did not link. Those with continuous and discontinuous Medicaid enrollment had a 1.91 (95% CI 1.84 to 1.99) and 3.32 (95% CI 3.19 to 3.45) times higher hazard of death, respectively, vs. those not linked to Medicaid. Similar patterns were consistently observed for specific cancer types. Conclusions: These results confirm an insurance-associated disparity in a national sample of young adult cancer patients and provide additional information on risks in association with Medicaid enrollment continuity. These results further support the critical need for consistent health insurance coverage in young adults and for additional research to understand social, economic, and access-related factors leading to lower survival in the Medicaid population. Lowering administrative burdens for Medicaid enrollment, eligibility, and renewal are potentially important strategies for improving cancer outcomes.