Adherence to lifesaving antiretroviral therapy (ART) for HIV infection remains a challenge for many patients. Routine screening for barriers to ART adherence could help make HIV care more patient-centered and prevent virologic rebound or failure. Our team is currently developing a new HIV-specific patient-reported outcome measure (PROM) of these barriers for use in Canada and France along with a digital app for its electronic administration. In our previous work, we developed the PROM's multidimensional conceptual framework and generated 100 English items, which have been translated to French.This study aims to use a Web-based Delphi to help validate and select the content of this new HIV-specific PROM, based on the perspective of anglophone and francophone patients and providers in Canada and France. Here, we present the proposal for this Delphi.This modified Delphi will involve a diverse panel of patients (n=32) and providers (n=52) recruited especially from the 9 sites of the PROM development study (site locations in Canada: Montreal, Toronto, Vancouver; in France: Paris, Nantes, Clermont-Ferrand, Saint-Martin, Cayenne). Overall, 2 rounds of Web-based questionnaires will be conducted. The threshold for consensus is set at 60% and will determine which items are carried forward to the second round. Per item, 3 aspects will be rated: importance as a barrier to ART adherence, relevance for HIV care, and clarity. In both rounds, space will be available for free text comments. Overall comprehensiveness will be assessed in the second round.This study has undergone a methodological review by experts in patient-oriented research. It has received approval from a research ethics board of the McGill University Health Centre. It is financially supported, in part, by the Canadian Institutes of Health Research's Strategy for Patient-Oriented Research-Quebec Support Unit (M006). As of May 21, 2019, 15 people living with HIV and 25 providers completed the first round of the Delphi (24 from Canada and 16 from France).To our knowledge, this is the first Delphi to seek consensus on the most relevant and clinically actionable barriers to ART adherence, collecting opinions on an extensive list of barriers. Drawing on a relatively large and diverse panel of HIV patients and providers, it essentially engages key stakeholders in decision making about the PROM's final content, helping to ensure its utility and adoption.PRR1-10.2196/12836.