Purpose: Medicaid expansion in 2014 is associated with improved insurance coverage and stage at diagnosis in cancer patients. However, little is known about the effect of early Medicaid expansions in 2010 to 2011 on outcomes in radiation therapy recipients. The objective of this study was to estimate the effect of early Medicaid expansion on insurance status and stage at diagnosis among radiation therapy recipients. Methods and Materials: The Surveillance, Epidemiology, and End Results database was queried for cases aged 18 to 64 diagnosed in 2007 to 2013 with a first primary malignancy treated with radiation therapy. Difference-in-differences analyses were used to compare changes in insurance coverage and stage at diagnosis from 2007 to 2009 and 2011 to 2013 in expansion relative to nonexpansion states. Results: There was a –0.48 (95% confidence interval [CI], –0.84 to –0.13; P =.007) percentage point (PP) reduction in uninsured in expansion relative to nonexpansion states, primarily among counties with lower educational attainment (–1.73 PP; 95% CI, –2.72 to –0.75). Increases in early stage diagnoses in expansion relative to nonexpansion states were found overall and in breast (1.56 PP; 95% CI, 0.45-2.68; P =.006), colorectal (3.72 PP; 95% CI, 0.33-7.12; P =.032), and lung (1.49 PP; 95% CI, 0.25-2.72; P =.018) cancers. Decreases in late stage diagnoses were found in cervical (–5.91 PP; 95% CI, –9.58 to –2.25; P =.002), colorectal (–2.72 PP; 95% CI, –5.43 to –0.01; P =.05), and lung (–3.28 PP; 95% CI, –5.47 to –1.1; P =.003) cancers. Conclusions: For radiation therapy recipients, early Medicaid expansion was associated with decreased percent uninsured, particularly among low education counties, and earlier stage diagnoses for screenable cancers. Thus, early Medicaid expansion may improve access to care and decrease disparities for radiation therapy recipients.