Background: Adolescents and Young Adults (AYAs), aged 15-39, experience unique challenges in cancer care. Frequent health insurance gaps for this population due to age, employment, and living changes hinder effective care and outcome assessments. Uninsured AYAs have lower survival rates, and insurance disparities are notable among Black, Hispanic, and rural patients; however, patterns of enrollment among AYAs have not been well described. Our study examined these patterns using insurance claims data to better inform AYA cancer care and outcomes. Methods: We conducted a retrospective cohort study with the Cancer Information and Population Health Resource (CIPHR), a linkage of cancer registry data and private and public payer data in North Carolina, including Medicaid and over 70% of the private insurance market. We included patients aged 15-39 diagnosed with common AYA cancers (leukemia, lymphoma, breast cancer, melanoma, sarcoma, germ cell tumors) from 2003-2019, linked to claims from 2003-2020. We analyzed insurance coverage patterns, comparing continuous enrollment 1) from two months pre-diagnosis to 12 months post-diagnosis and 2) from the month of diagnosis through 12 months. We compared demographics, clinical characteristics, and insurance types across scenarios. Results: The full cancer registry cohort included 21,060 AYAs; 11,024 (52.3%) had no link to Medicaid or private insurance in the year of cancer diagnosis. Continuous enrollment was 4,707 (22.4%) from two months prior through 12 months after, increasing to 5,912 (28.1%) for month of diagnosis through 12 months, particularly among Medicaid beneficiaries (from 10.8% to 15.6% of total cohort). Less restrictive criteria increased representation among Black (from 29.1% to 38.5%) and rural patients (from 25.2% to 33.1%) and those with leukemia (25.2% to 33.8%) and lymphoma (24.0% to 31.0%). Conclusions: AYAs face substantial hurdles with discontinuous insurance coverage around their cancer diagnosis. Claims-based research can characterize cancer care delivery, and use of less restrictive eligibility criteria expands the generalizability of findings to a more diverse cohort of AYAs. Increasing health insurance coverage over time may be due to the Affordable Care Act. Medicaid expansion within our state is likely to further improve access for AYAs. Continued efforts are essential to help AYAs with cancer secure necessary insurance coverage.