Background: Mental health treatment is scarce and little resources are invested in reducing the wide treatment gap that exists in the Americas. The regional barriers are unknown. We describe the barriers for not seeking treatment among those with mental and substance use disorders from six (four low- and middle-income and two high-income) countries from the Americas. Regional socio-demographic and clinical correlates are assessed. Methods: Respondents (n = 4648) from seven World Mental Health surveys carried out in Argentina, Brazil, Colombia, Mexico, Peru, and the United States, who met diagnostic criteria for a 12-month mental disorder, measured with the Composite International Diagnostic Interview, and who did not access treatment, were asked about treatment need and, among those with need, structural and attitudinal barriers. Country-specific deviations from regional estimates were evaluated through logistic models. Results: In the Americas, 43% of those that did not access treatment did not perceive treatment need, while the rest reported structural and attitudinal barriers. Overall, 27% reported structural barriers, and 95% attitudinal barriers. The most frequent attitudinal barrier was to want to handle it on their own (69.4%). Being female and having higher severity of disorders were significant correlates of greater perceived structural and lower attitudinal barriers, with few country-specific variations. Limitations: Only six countries in the Americas are represented; the cross-sectional nature of the survey precludes any causal interpretation. Conclusions: Awareness of disorder or treatment need in various forms is one of the main barriers reported in the Americas and it specially affects persons with severe disorders.