Following the June 2012 Supreme Court ruling that states are no longer mandated to expand their Medicaid programs in 2014 as part of the Affordable Care Act, many states plan to opt out of the expansion, citing affordability as their primary concern. In response to this controversy, the present study evaluated the cost savings of expanding Medicaid coverage to include currently ineligible homeless adults with substance use disorders, a subset of the population that incurs some of the greatest societal costs and is disproportionately impacted by uninsurance. Using a time horizon of 7 years, separate analyses were conducted for state and federal governments, and then a final analysis evaluated the combined costs for the other two models. Results of the study demonstrate that, although the expansion will be associated with a net cost when combining state and federal expenses and savings, states will experience tremendous savings if they choose to participate.