BackgroundOpioid misuse is a large public health problem in the United States. Residents of rural areas and American Indian (AI) reservation/trust lands represent traditionally underserved populations with regard to substance-use disorder therapy. PurposeAssess differences in the number of opioid agonist therapy (OAT) facilities and physicians with Drug Addiction Treatment Act (DATA) waivers for rural versus urban, and AI reservation/trust land versus non-AI reservation/trust land areas in Washington State. MethodsThe unit of analysis was the ZIP code. The dependent variables were the number of OAT facilities and DATA-waivered physicians in a region per 10,000 residents aged 18-64 in a ZIP code. A region was defined as a ZIP code and its contiguous ZIP codes. The independent variables were binary measures of whether a ZIP code was classified as rural versus urban, or AI reservation/trust land versus non-AI reservation/trust land. Zero-inflated negative binomial regressions with robust standard errors were estimated. ResultsThe number of OAT clinics in a region per 10,000 ZIP-code residents was significantly lower in rural versus urban areas (P = .002). This did not differ significantly between AI reservation/trust land and non-AI reservation/trust land areas (P = .79). DATA-waivered physicians in a region per 10,000 ZIP-code residents was not significantly different between rural and urban (P = .08), or AI reservation/trust land versus non-AI reservation/trust land areas (P = .21). ConclusionsIt appears that the potential for Washington State residents of rural and AI reservation areas to receive OAT is similar to that of residents outside of those areas; however, difficulties in accessing therapy may remain, highlighting the importance of expanding health care insurance and providing support for DATA-waivered physicians.