States must offer Medicaid coverage to low-income adults with disabilities; however, they have discretion in the design of eligibility criteria and enrollment processes. Using the American Community Survey, we examined the health insurance status of adults enrolled in the Supplemental Security Income (SSI) disability program including (1) the national rate of health insurance coverage; (2) state rates of uninsurance and Medicaid; and (3) the correlates of uninsurance. Uninsurance and Medicaid rates varied across states from 1% to 12% and from 63% to 91%, respectively. Nationally, 5% of the SSI population was uninsured; 77% was enrolled in Medicaid. Limited English proficiency, Black race, lack of U.S. citizenship, and residence in a state that used an enrollment process and/or eligibility criteria distinct from the SSI program were associated with uninsurance. As states streamline Medicaid enrollment processes to meet requirements of the Affordable Care Act, they should consider the needs of this vulnerable population.