Population-based cancer registries collect information on first course of treatment that may be utilized in research on cancer care quality, yet few studies have investigated the validity of this information. We examined the accuracy and completeness of registry-based treatment information in a cohort of adolescent and young adult women. Women diagnosed with breast cancer, lymphoma, thyroid cancer, cervical/uterine cancer or ovarian cancer at ages 15-39 during 2003-2014 were identified using data from the North Carolina Central Cancer Registry (CCR) (N = 2342). CCR data were linked to Medicaid and private insurance claims data, and claims were reviewed for the 12 months following diagnosis to identify cancer treatments received. Using claims data as the gold standard, we calculated the sensitivity and positive predictive value (PPV) of CCR data for receipt of chemotherapy, radiation and hormone therapy. We also compared dates of treatment initiation between the two data sources. For all cancer types combined, the sensitivity of the CCR data was high for chemotherapy (86%) and moderate for radiation (74%). PPVs were 82% and 83% for chemotherapy and radiation, respectively. Both the sensitivity (67%) and PPV (70%) were lower for hormone therapy for breast cancer. For all three treatment types, dates of initiation in the registry and the claims differed by ≤30 days for most women. In this cohort of young women, population-based cancer registry data on chemotherapy receipt was reasonably accurate and complete in comparison with insurance claims. Radiation and hormone therapy appeared to be less complete.