A large number of adults with substance use disorder (SUD) do not receive treatment for their condition. Using data from the 2008-2013 National Survey of Drug Use and Health (NSDUH), this study analyzes why individuals with SUD report not receiving treatment even when they perceived a need for it. It further examines the variations in reported reasons for not receiving treatment by health insurance status and type. The results suggest that barriers such as stigma, lack of readiness to stop using substances, and not making treatment a priority are more common among the insured population, especially among those with private insurance. Financial barriers, such as not being able to afford the cost of treatment, are more prominent among the uninsured population. Efforts to improve utilization of treatment services will need to address financial as well as barriers related to stigma.